Magnetic material, method for producing magnetic material, and inductor element

ABSTRACT

A magnetic material is disclosed, which includes magnetic particles containing at least one magnetic metal selected from the group including Fe, Co and Ni, and at least one non-magnetic metal selected from Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, rare earth elements, Ba and Sr; a first coating layer of a first oxide that covers at least a portion of the magnetic particles; oxide particles of a second oxide that is present between the magnetic particles and constitutes an eutectic reaction system with the first oxide; and an oxide phase that is present between the magnetic particles and has an eutectic structure of the first oxide and the second oxide.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2011-189070, filed on Aug. 31, 2011, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a magnetic material, amethod for producing a magnetic material, and an inductor element.

BACKGROUND

Currently, magnetic materials are applied to various devices such asinductor elements, electromagnetic wave absorbers, magnetic inks, andantenna apparatuses, and are considered as very important materials.These components utilize the characteristics of the real part of themagnetic permeability (real part of the relative permeability) μ′ or theimaginary part of the magnetic permeability (imaginary part of therelative permeability) μ″ carried by magnetic materials, in accordancewith the purpose. For example, inductance elements or antennaapparatuses utilize high μ′ (and low μ″), while electromagnetic waveabsorbers utilize high μ″. Accordingly, when such components areactually used as devices, the characteristics μ′ and μ″ should becontrolled in accordance with the frequency band of use of theequipment.

In recent years, an adjustment of the frequency band of use of theequipment to higher frequencies is underway, and thus there is an urgentneed for the development of a magnetic material having excellentcharacteristics with high μ′ and low μ″ at high frequencies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the magnetic material of a firstembodiment;

FIG. 2 is a schematic diagram of the magnetic material of a firstmodification of the first embodiment;

FIG. 3 is a schematic diagram of the magnetic material of a secondmodification of the first embodiment;

FIG. 4 is a schematic diagram of the magnetic material of a secondembodiment;

FIG. 5 is a schematic diagram of the magnetic material of a fifthembodiment;

FIG. 6 is a schematic diagram of the magnetic material of a sixthembodiment;

FIG. 7 is a schematic diagram of the magnetic material of a seventhembodiment;

FIG. 8 is a schematic diagram of the magnetic material of a firstmodification of the seventh embodiment;

FIG. 9 is a schematic diagram of the magnetic material of a secondmodification of the seventh embodiment;

FIG. 10 is a schematic diagram of the magnetic material of an eighthembodiment;

FIG. 11 is a schematic diagram of the magnetic material of amodification of the eighth embodiment;

FIG. 12A and FIG. 12B are conceptual diagrams of the device of a tenthembodiment;

FIG. 13A and FIG. 13B are conceptual diagrams of the inductor element ofthe tenth embodiment;

FIG. 14 is a conceptual diagram of the inductor element of the tenthembodiment; and

FIG. 15 is a diagram exhibiting the frequency characteristics ofmagnetic permeabilities (μ′ and μ″) of Example 3.

DETAILED DESCRIPTION

The magnetic material of the embodiments includes magnetic particlescontaining at least one magnetic metal selected from a group consists ofiron (Fe), cobalt (Co) and nickel (Ni), and at least one non-magneticmetal selected from the group including magnesium (Mg), aluminum (Al),silicon (Si), calcium (Ca), zirconium (Zr), titanium (Ti), hafnium (Hf),zinc (Zn), manganese (Mn), rare earth elements, barium (Ba) andstrontium (Sr); a first coating layer of a first oxide that covers atleast a portion of the magnetic particles; oxide particles of a secondoxide that are present between the magnetic particles and constitute aneutectic reaction system with the first oxide; and an oxide phase thatis present between the magnetic particles and has an eutectic structureof the first oxide and the second oxide.

Magnetic materials having high μ′ and low μ″ have recently attractedattention in connection with the application thereof to power inductanceelements used in power semiconductors. In recent years, the importanceof energy saving and environmental protection has been activelyadvocated, and a reduction of the CO₂ emission and a reduction of thedependency on fossil fuels have become indispensable.

As a result, the development of electric cars or hybrid cars tosubstitute gasoline cars is in active progress. Furthermore, thetechnologies for utilizing natural energies such as solar powergeneration and wind power generation are regarded as the keytechnologies for an energy-saving society, and various developedcountries have actively promoted the development of technologies forutilizing natural energies. Furthermore, as an environment-friendlyelectric power saving system, the importance of establishment of homeenergy management systems (HEMS) and building and energy managementsystems (BEMS) that control the electric power generated by solar powergeneration, wind power generation and the like through smart grids, andsupply the electric power to homes, offices and industrial plants athigh efficiency, is being actively advocated.

In such a trend of energy savings, power semiconductors play animportant role. Power semiconductors are semiconductors which controlhigh electric power or energy with high efficiency, and include powerdiscrete semiconductors such as insulated gate bipolar transistors(IGBTs), metal oxide semiconductor field-effect transistors (MOSFETs),power bipolar transistors, and power diodes, as well as power supplycircuits such as linear regulators and switching regulators, and logiclarge-scale integration (LSI) for power management to control thesedevices.

Power semiconductors are widely used in all the equipment in theapplications of electrical appliances, computers, automobiles, and railtransportation, and an increase in the supply of these appliedinstruments and an increase in the mounting ratio of powersemiconductors in these instruments can be expected. Therefore, a rapidgrowth in the market for power semiconductors in the future isanticipated. For example, in the inverters that are mounted in manyelectrical appliances, power semiconductors are used to an extent thatmay be said to be almost the entirety, and extensive energy saving ismade possible thereby.

Currently, silicon (Si) constitutes the mainstream of powersemiconductors; however, for the purpose of increasing the efficiency orminiaturizing instruments, it is believed to be effective to use SiC andGaN. SiC or GaN has a large band gap or a large dielectric breakdownelectric field and can increase the withstand voltage, and thus, SiC andGaN can decrease the thickness of elements. Therefore, the on-resistanceof semiconductors can be decreased, and the substances are effective inreducing losses and increasing efficiency. Also, since SiC or GaN has ahigh degree of carrier mobility, the switching frequency can beincreased to high frequencies, and it is effective in theminiaturization of elements. Particularly, since SiC has higher heatconductivity than Si does, SiC has high heat dissipation capacity andenables operation at high temperatures. Thus, the cooling mechanism canbe simplified, and miniaturization is effectively achieved.

From the viewpoints described above, the development of SiC and GaNpower semiconductors is in active progress. However, in order to realizethe development, the development of power inductor elements that areused together with power semiconductors, that is, the development ofhigh-permeability magnetic materials (high μ′ and low μ″), isindispensable. At this time, the characteristics required in magneticmaterials include high magnetic permeability in the driving frequencyband, low magnetic loss, as well as high saturation magnetizationcapable of coping with large currents. If the saturation magnetizationis high, even if a high magnetic field is applied, magnetic saturationdoes not easily occur, and an effective decrease in the inductance valuecan be suppressed. Thereby, the direct current superimpositioncharacteristics of devices are enhanced, and the efficiency of systemsis enhanced.

Examples of a magnetic material for systems in the several kW class at10 kHz to 100 kHz include Sendust (Fe—Si—Al), nanocrystalline Finemet(Fe—Si—B—Cu—Nb), ribbons and compressed powders of Fe group/Co groupamorphous glass, and MnZn-based ferrite materials. However, all of themdo not completely satisfy characteristics such as high magneticpermeability, low loss, high saturation magnetization, high thermalstability, and high oxidation resistance, and are therefore notsatisfactory.

Furthermore, it is ascertained that the driving frequency of systemswill be further adjusted to higher frequencies in the future, along withthe popularization of SiC and GaN semiconductors, and characteristicssuch as high magnetic permeability and low loss in the megaherz (MHz)range of 100 kHz or higher are required. However, no such magneticmaterial exists for now. Therefore, the development of a magneticmaterial which satisfies high magnetic permeability and low loss in theMHz range of 100 kHz or higher, while satisfying high saturationmagnetization, high thermal stability, and high oxidation resistance, isindispensable.

Furthermore, a magnetic material having high μ′ and low μ″ at highfrequencies is expected to be applicable to the devices of highfrequency communication equipment, such as antenna apparatuses. As amethod of reducing the size of antennas and saving more electric power,there is available a method of dragging electromagnetic waves that reachan electronic component or a substrate in communication equipment froman antenna by using an insulating substrate having high magneticpermeability (high μ′ and low μ″) as an antenna substrate, and achievingtransmission and reception of electromagnetic waves without causing theelectromagnetic waves to reach the electronic component or substrate.Thereby, miniaturization of antennas and electric power savings areenabled, and at the same time, broadbanding the resonance frequency ofantennas is also enabled, which is preferable.

Even in such applications, in the event that a magnetic material forpower inductor elements described above has been developed, the magneticmaterial can be applied, and therefore, it is preferable.

Furthermore, in electromagnetic wave absorbers, the noise generated fromelectronic equipment is absorbed, and inconveniences such asmalfunctions of electronic equipment is reduced, by utilizing high μ″.Examples of the electronic equipment include semiconductor elements suchas integrated circuit (IC) chips, and various communication instruments.Such electronic equipment is used in various frequency bands, and thus,high μ″ at a predetermined frequency band is demanded. In general, amagnetic material has high μ″ near a ferromagnetic resonance frequency.However, if various magnetic losses other than a ferromagnetic resonanceloss, for example, an eddy current loss, a domain wall resonance lossand the like can be suppressed, μ″ can be decreased while μ′ can beincreased in a frequency band sufficiently lower than the ferromagneticresonance frequency.

That is, even a single material can be used as a high-permeabilitycomponent or can be used as an electromagnetic wave absorber, bychanging the frequency band of use. Therefore, in the event that amagnetic material for power inductors described above has beendeveloped, even in an application for electromagnetic wave absorbersutilizing μ″, there is a possibility that the magnetic material can beapplied by adjusting the ferromagnetic resonance frequency to thefrequency band of use.

On the other hand, a material that is developed as an electromagneticwave absorber is usually designed to maximize μ″ by summing up variousmagnetic losses such as the ferromagnetic resonance loss, the eddycurrent loss, and the domain wall resonance loss. For this reason, it isdifficult to use a material that is developed as an electromagnetic waveabsorber, in high-permeability components for inductor elements orantenna apparatuses (high μ′ and low μ″) at any of all frequency bands.

Meanwhile, electromagnetic wave absorbers are conventionally producedaccording to a binder molding method of mixing ferrite particles,carbonyl iron particles, FeAlSi flakes, FeCrAl flakes and the like witha resin. However, all of these materials have extremely low μ′ and μ″ inhigh frequency bands, and do not necessarily give satisfactorycharacteristics. In addition, materials that are synthesized by amechanical alloying method or the like have a problem that the long-termthermal stability is insufficient, and the product yield is low.

As discussed above, various materials have been suggested hitherto asthe magnetic materials used in power inductor elements, antennas, andelectromagnetic wave absorbers, but all of the materials do not satisfythe required material characteristics.

Hereinafter, the embodiments will be explained using the attacheddrawings. Identical or similar symbols have been assigned to theidentical or similar parts in the drawings.

First Embodiment

The magnetic material of the current embodiment contains magneticparticles containing at least one magnetic metal selected from a groupconsists of Fe, Co and Ni, and at least one non-magnetic metal selectedfrom Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, rare earth elements, Ba and Sr;a first coating layer of a first oxide that covers at least a portion ofthese magnetic particles; oxide particles of a second oxide that arepresent between the magnetic particles and constitute an eutecticreaction system with the first oxide; and an oxide phase that is presentbetween the magnetic particles and contains an eutectic structure of thefirst oxide and the second oxide.

The magnetic material of the current embodiment realizes high magneticpermeability and low loss in the MHz range of 100 kHz or higher, byhaving the constitution described above. Furthermore, the magneticmaterial also makes it possible to realize high saturationmagnetization, high thermal stability, and high oxidation resistance.

FIG. 1 is a schematic diagram of the magnetic material of the currentembodiment. The magnetic material of the current embodiment is composedof magnetic particles 10; a first coating layer 12 of a first oxide thatcovers these magnetic particles 10; oxide particles 14 of a second oxidethat are present between the magnetic particles 10; and an oxide phase16 formed from an eutectic structure of the first oxide and the secondoxide.

The magnetic particles 10 contains at least one magnetic metal selectedfrom a group consists of Fe (iron), Co (cobalt) and Ni (nickel), and atleast one non-magnetic metal selected from Mg, Al, Si, Ca, Zr, Ti, Hf,Zn, Mn, rare earth elements, Ba and Sr. The magnetic particles 10 areformed from an alloy containing, for example, Fe, Co and Al (aluminum),or an alloy containing Fe, Ni, or Si (silicon).

The first oxide and the second oxide constitute an eutectic reactionsystem. That is, the first oxide and the second oxide produce aneutectic crystal. The first oxide is, for example, Si (silicon)-systemoxide, and the second oxide is, for example, B (boron)-system oxide.

The first coating layer 12 that covers at least a portion of themagnetic particles 10 is formed of a first oxide. Furthermore, the oxideparticles 14 that are present between the magnetic particles 10 areformed of a second oxide.

The oxide phase 16 that is present between the magnetic particles 10 isformed from the first oxide and the second oxide, and has an eutecticstructure of the first oxide and the second oxide. The eutecticstructure as used herein is a solidification structure produced by aneutectic reaction, and is a structure based on a layered (lamellar)eutectic structure in which two kinds of crystals are alternatelyarranged in layers, a rod-shaped eutectic structure in which crystalsare arranged in a rod shape, or a helical eutectic structure in whichcrystals are arranged in a helical shape. At this time, for example, thespacing between the individual layers (or rods) of the layeredstructure, rod-shaped structure and helical structure is dependent onthe eutectic composition, or the solidification conditions such assolidification rate.

According to the current embodiment, when the magnetic particles 10 aresurrounded by the oxide phase 16 having an eutectic structure,aggregation of the magnetic particles 10 is suppressed, and thus amagnetic material which is thermally stable and has high oxidationresistance is realized. Therefore, deterioration of magneticcharacteristics is suppressed.

Furthermore, the oxide phase 16 having an eutectic structure also hashigh mechanical strength. For this reason, cracking or damage does noteasily occur when the material is subjected to a thermal cycle or underload, and the thermal stability or oxidation resistance of the magneticmaterial can be enhanced.

Furthermore, since the oxide phase 16 can be formed by an eutecticreaction between the first oxide and the second oxide, an oxide phase 16having high strength at a relatively low temperature can be formed.Therefore, the magnetic material of the current embodiment can beproduced by a process at a relatively low temperature. Therefore,according to the current embodiment, oxidation, modification or the likeof the magnetic particles 10 during the production process can besuppressed.

According to the current embodiment, thermal stability and oxidationresistance can be further enhanced by leaving a first oxide which has ahigh melting point in a simple form, as the first coating layer 12, andleaving a second oxide which has a high melting point, as the oxideparticles, between the magnetic particles 10, in addition to the oxidephase 16.

The magnetic particles 10 are such that when the particles arespherical, the average particle size is preferably from 50 nm to 50 μm.If the particle size of the magnetic particles 10 is too large, thecoercive force decreases, which is preferable. On the other hand, whenthe electrical resistivity of the magnetic particles 10 is small, if theparticle size is too large, the eddy current loss becomes large, whichis not preferable. On the contrary, if the particle size of the magneticparticles 10 is too small, the eddy current loss becomes small, which ispreferable; however, the coercive force becomes large, and it is notpreferable.

Meanwhile, the magnetic loss of the magnetic material is mainly composedof three components such as an eddy current loss, a hysteresis loss, anda ferromagnetic resonance loss, and it is preferable that all the threecomponents be low. Among these, the hysteresis loss is a lossattributable to the coercive force of the magnetic material, and if thecoercive force increases, the hysteresis loss increases when themagnetic field applied to the magnetic material is increased, which isnot preferable. The discussion on the average particle size as describedabove is a discussion concerning the optimum particle size forminimizing the sum of the eddy current loss and the hysteresis loss, andthe optimum particle size range varies with the frequency band used. Theoptimum average particle size for minimizing the sum of the eddy currentloss and the hysteresis loss in the MHz range of 100 kHz or higher, isfrom 50 nm to 50 μm.

Furthermore, the magnetic particles 10 may be spherical, but it is morepreferable that the magnetic particles have a flat shape or a rod shape,which has a large aspect ratio. The rod shape also includes spheroid.

Here, the “aspect ratio” means the ratio of the dimension of a particlein a direction in which the length of the particle is the longest (longdimension) and the dimension of the particle in a direction that isperpendicular to the above-described direction, in which the length ofthe particle is the shortest (short dimension), that is, the ratio of“long dimension/short dimension”. Therefore, the aspect ratio is always1 or greater. In the case of a perfect sphere, the long dimension andthe short dimension are both identical to the diameter of the sphere,and therefore, the aspect ratio is 1. The aspect ratio of a flat-shapedparticle is the diameter (long dimension)/height (short dimension). Theaspect ratio of a rod shape is the length of the rod (longdimension)/the diameter of the bottom of the rod (short dimension).However, the aspect ratio of a spheroid is the major axis (longdimension)/minor axis (short dimension). When the aspect ratio isincreased, shape magnetic anisotropy can be added, and by aligning thedirections of the axes of easy magnetization into one direction, themagnetic permeability and the high frequency characteristics of magneticpermeability can be enhanced. Meanwhile, the value obtained by averagingthe aspect ratios of plural particles is called an “average aspectratio.” Furthermore, the values obtained by averaging the longdimensions and short dimensions in plural particles are called an“average long dimension” and an “average short dimension.”

Meanwhile, if the aspect ratio is large, shape-induced magneticanisotropy is added. Therefore, when a desired magnetic material isproduced by integrating the magnetic particles 10, the magneticparticles can be easily oriented by the magnetic field. Also, when theaspect ratio is increased, in the case where a desired magnetic materialis produced by integrating the magnetic particles 10, the packing ratioof the magnetic particles 10 can be increased as compared with the caseof integrating spherical magnetic particles. Therefore, the saturationmagnetization of the magnetic material per weight or the saturationmagnetization per volume can be increased, and as a result, the magneticpermeability can also be increased.

Meanwhile, in the cases of flat-shaped and rod-shaped particles, it ispreferable that the average height (in the case of a rod shape, theaverage diameter) be from 10 nm to 2 μm, and more preferably, it ispreferable that the average height (in the case of a rod shape, theaverage diameter) be from 10 nm to 100 nm. A larger average aspect ratiois more preferable, and the average aspect ratio is preferably 5 orgreater, and more preferably 10 or greater. These are sizes appropriatefor minimizing the sum of the eddy current loss and the hysteresis lossin the MHz range of 100 kHz or greater.

It is desirable that the volume ratio of the magnetic particles 10 inthe magnetic material occupy a volume ratio of from 10% to 70% relativeto the total volume of the magnetic material. If the volume ratioexceeds 70%, the electrical resistivity of the magnetic material issmall, the eddy current loss increases, and there is a risk that thehigh frequency magnetic properties would deteriorate. If the volumeratio is adjusted to less than 10%, when the volume fraction of themagnetic metal is lowered, the saturation magnetization of the magneticmaterial is decreased, and there is a risk that the magneticpermeability would be decreased thereby.

The magnetic metal contained in the magnetic particles 10 includes atleast one selected from the group including Fe, Co, and Ni, andparticularly, Fe-based alloys, Co-based alloys, FeCo-based alloys, andFeNi-based alloys are preferred because these alloys can realize highsaturation magnetization. Fe-based alloys contain Ni, Mn, Cu and thelike as a second component, and examples thereof include FeNi alloys,FeMn alloys, and FeCu alloy. Co-based alloys contain Ni, Mn, Cu and thelike as a second component, and examples thereof include CoNi alloys,CoMn alloys, and CoCu alloys. FeCo-based alloys include Ni, Mn, Cu andthe like as a second component.

These second components are components that are effective in enhancingthe high-frequency magnetic properties of the magnetic particles 10.Since FeNi-based alloys have small magnetic anisotropy, these arematerials advantageous for obtaining high magnetic permeability.Particularly, a FeNi alloy having Fe in a proportion of from 40 atom %to 60 atom % has high saturation magnetization and has low anisotropy,and therefore, this alloy is preferred.

Among the magnetic metals, it is preferable to use a FeCo-based alloy.The amount of Co in FeCo is preferably adjusted to an amount of from 10atom % to 50 atom %, from the viewpoint of satisfying thermal stability,oxidation resistance, and a saturation magnetization of 2 teslas orgreater. A more preferred amount of Co in FeCo is in the range of from20 atom % to 40 atom %, from the viewpoint of further increasing thesaturation magnetization.

The magnetic particles 10 preferably contain a non-magnetic metal as inthe case of the current embodiment. In this case, it is preferable thatthe magnetic metal and the non-magnetic metal contained in the magneticparticles 10 form a solid solution with each other. By forming a solidsolution, mechanical strength, thermal stability and oxidationresistance can be increased.

The non-magnetic material is at least one metal selected from Mg, Al,Si, Ca, Zr, Ti, Hf, Zn, Mn, rare earth elements, Ba, and Sr. Thesenon-magnetic metals can increase the electrical resistivity of themagnetic particles 10, and can enhance thermal stability and oxidationresistance. Among them, Al and Si are preferred because these elementscan easily form solid solutions with Fe, Co and Ni, which are the maincomponents of metal nanoparticles, and contribute to an enhancement ofthermal stability of the magnetic particles.

In regard to the amount of the non-magnetic metal, it is preferable thatthe magnetic material contain the non-magnetic metal in an amount offrom 0.001 atom % to 20 atom % based on the magnetic metal. If thecontent of the non-magnetic metal is greater than 20 atom %, there is arisk that the saturation magnetization of the magnetic particles bedecreased. A more preferred amount from the viewpoints of highsaturation magnetization and solid solution properties is in the rangeof from 0.001 atom % to 5 atom %, and even more preferably from 0.01atom % to 5 atom %.

Particularly, it is preferable that in the magnetic particles 10containing a FeCo-based alloy as a magnetic metal and at least oneelement selected from Al and Si as a non-magnetic metal, the at leastone element selected from Al and Si (if co-present, the sum of therespective contents) be incorporated in an amount in the range of from0.001 atom % to 5 atom %, and more preferably from 0.01 atom % to 5 atom%, with reference to FeCo. Thereby, saturation magnetization, thermalstability and oxidation resistance in particular can be maintained at asatisfactory level.

As the crystal structure of the magnetic particles 10, a body-centeredcubic lattice structure (bcc), a face-centered cubic lattice structure(fcc), and a hexagonal close-packed structure (hcp) can be considered,and each of them has unique features. The bcc structure is advantageousin that since a composition having a large proportion of a Fe-basedalloy has the bcc structure, the bcc structure can be easily synthesizedin a wide variety. The fcc structure is advantageous in that since thediffusion coefficient of the magnetic metal can be made smaller ascompared to that of the bcc structure, thermal stability or oxidationresistance can be made relatively larger. The hcp structure (hexagonalstructure) is advantageous in that the magnetic characteristics of themagnetic material can be made to exhibit in-plane uniaxial anisotropy.Since a magnetic metal having the hcp structure generally has highmagnetic anisotropy, it is easy to orient the magnetic metal, and themagnetic permeability can be made large. Particularly, Co-based alloyseasily acquire the hcp structure and are preferred. In the case of aCo-based alloy, since the alloy can stabilize the hcp structure bycontaining Cr or Al, it is preferable.

Meanwhile, in a magnetic material having in-plane uniaxial anisotropy,the in-plane uniaxial anisotropic magnetic field is preferably from 1 Oeto 5000 Oe, and more preferably from 10 Oe to 500 Oe. This is apreferred range to maintain low loss and high magnetic permeability inthe MHz range of 100 kHz or higher. If anisotropy is too low, theferromagnetic resonance frequency occurs at a low frequency, and a largeloss occurs in the MHz range, which is not preferable.

On the other hand, if anisotropy is high, the ferromagnetic resonancefrequency is high, and a low loss can be realized; however, the magneticpermeability becomes small. The range of an anisotropic magnetic fieldwhich can achieve a balance between high magnetic permeability and lowloss is from 1 Oe to 500 Oe, and more preferably from 10 Oe to 500 Oe.

Meanwhile, in order to induce in-plane uniaxial anisotropy in a magneticmaterial, there is a method of orienting magnetic particles having thehcp structure, as well as a method of inducing magnetic anisotropy inany one direction in the plane by means of a magnetic field or strain,by making the crystallinity of the magnetic particles 10 amorphous asmuch as possible. For this reason, it is preferable to employ acomposition which can make the magnetic particles amorphous as easily aspossible.

From such a viewpoint, it is preferable that the magnetic metalcontained in the magnetic particles 10 include at least one additivemetal selected from B, Si, C, Ti, Zr, Hf, Nb, Ta, Mo, Cr, Cu and W,which are different from the non-magnetic metal, altogether in an amountof from 0.001 atom % to 25 atom % relative to the total amount of themagnetic metal, non-magnetic metal and additive metal, and that at leasttwo of the magnetic metal, the non-magnetic metal, and the additivemetal form a solid solution with each other.

Examples of the combination of the first oxide and the second oxide(first oxide-second oxide, or second oxide-first oxide) according to thecurrent embodiment include B₂O₃—SiO₂, B₂O₃—Cr₂O₃, B₂O₃—MoO₃, B₂O₃—Nb₂O₅,B₂O₃—Li₂O₃, B₂O₃—BaO, B₂O₃—ZnO, B₂O₃—La₂O₃, B₂O₃—P₂O₅, B₂O₃—Al₂O₃,B₂O₃—GeO₂, B₂O₃—WO₃, B₂O₃, Cs₂O₃, B₂O₃—K₂O, Na₂O—SiO₂, Na₂O—B₂O₃,Na₂O—P₂O₅, Na₂O—Nb₂O₅, Na₂O—WO₃, Na₂O—MoO₃, Na₂O—GeO₂, Na₂O—TiO₂,Na₂O—As₂O₅, Na₂O—TiO₂, Li₂O—MoO₃, Li₂O—SiO₂, Li₂O—GeO₂, Li₂O—WO₃,Li₂O—V₂O₅, Li₂O—GeO₂, K₂O—SiO₂, K₂O₂—P₂O₅, K₂O—TiO₂, K₂O—As₂O₅, K₂O—WO₃,K₂O—MoO₃, K₂O—V₂O₅, K₂O—Nb₂O₅, K₂O—GeO₂, K₂O—Ta₂O₅, Cs₂O—MoO₃,Cs₂O—V₂O₅, Cs₂O—Nb₂O₅, Cs₂O—SiO₂, CaO—P₂O₅, CaO—B₂O₃, CaO—V₂O₅,ZnO—V₂O₅, BaO—V₂O₅, BaO—WO₃, Cr₂O₃—V₂O₅, ZnO—B₂O₃, PbO—SiO₂, andMoO₃—WO₃.

Among them, B₂O₃—SiO₂, B₂O₃—Cr₂O₃, B₂O₃—MoO₃, B₂O₃—Nb₂O₅, B₂O₃—Li₂O₃,B₂O₃—BaO, B₂O₃—ZnO, B₂O₃—La₂O₃, B₂O₃—P₂O₅, B₂O₃—Al₂O₃, B₂O₃—GeO₂,B₂O₃—WO₃, Na₂O—SiO₂, Na₂O—B₂O₃, Na₂O—P₂O₅, Na₂O—Nb₂O₅, Na₂O—WO₃,Na₂O—MoO₃, Na₂O—GeO₂, Na₂O—TiO₂, Na₂O—As₂O₅, Na₂O—TiO₂, Li₂O—MoO₃,Li₂O—SiO₂, Li₂O—GeO₂, Li₂O—WO₃, Li₂O—V₂O₅, Li₂O—GeO₂, CaO—P₂O₅,CaO—B₂O₃, CaO—V₂O₅, ZnO—V₂O₅, BaO—V₂O₅, BaO—WO₃, Cr₂O₃—V₂O₅, ZnO—B₂O₃,and MoO₃—WO₃ are preferred. The oxides of these combinations haverelatively low eutectic points, and produce eutectic crystals relativeeasily. Therefore, these combinations are preferred.

Particularly, a combination having an eutectic point of 1000° C. orlower is preferred. Furthermore, in regard to the combination of oxides,combinations of two or more oxides may also be employed, and preferableexamples include Na₂O—CaO—SiO₂, K₂O—CaO—SiO₂, Na₂O—B₂O₃—SiO₂,K₂O—PbO—SiO₂, BaO—SiO₂—B₂O₃, PbO—B₂O₃—SiO₂, and Y₂O₃—Al₂O₃—SiO₂.

Other preferable examples include La—Si—O—N, Ca—Al—Si—O—N, Y—Al—Si—O—N,Na—Si—O—N, Na—La—Si—O—N, Mg—Al—Si—O—N, Si—O—N, and Li—K—Al—Si—O—N.

An eutectic structure formed from such combinations of oxides asdescribed above is preferable because the structure forms a finestructure and gives a material that is strong in strength.

FIG. 2 is a schematic diagram of a first modification of the currentembodiment. The magnetic particles 10 are particle aggregates which havemetal nanoparticles 10 a having an average particle size of from 10 nmto 20 nm and containing at least one magnetic metal selected from thegroup including Fe, Co and Ni, and have a shape in which the averageshort dimension of from 10 nm to 2 μm and an average aspect ratio of 5or greater. Furthermore, the magnetic particles 10 contains anintermediate phase 10 b which is present between the metal nanoparticles10 a and contains at least one non-magnetic metal selected frommagnesium (Mg), aluminum (Al), silicon (Si), calcium (Ca), zirconium(Zr), titanium (Ti), hafnium (Hf), zinc (Zn), manganese (Mn), barium(Ba), strontium (Sr), chromium (Cr), molybdenum (Mo), silver (Ag),gadolinium (Ga), scandium (Sc), vanadium (V), yttrium (Y), niobium (Nb),lead (Pb), copper (Cu), indium (In), tin (Sn), and rare earth elements,and any one of oxygen (O), nitrogen (N) and carbon (C). The intermediatephase 10 b may contain fluorine (F). The intermediate phase 10 b is, forexample, a metal, a semiconductor, an oxide, a nitride, a carbide, or afluoride. Also, the intermediate phase 10 b has higher electricalresistivity than the magnetic particles 10.

In the current modification, the magnetic material is composed ofparticle aggregates having a nanogranular structure. A structure inwhich the intermediate phase 10 b fills the space between the metalnanoparticles 10 a, is established.

In such particle aggregates, the metal nanoparticles 10 a are likely tomagnetically bind to each other, and behave as a single aggregatemagnetically. On the other hand, since the intermediate phase 10 bhaving high electrical resistivity, for example, an oxide, is presentbetween the particles of the metal nanoparticles 10 a, the electricalresistivity of the magnetic particles 10 can be increased. Therefore, aneddy current loss can be suppressed while high magnetic permeability ismaintained.

The metal nanoparticles 10 a preferably have an average particle size offrom 1 nm to 20 nm. More preferably, the average particle size is from 1nm to 10 nm. If the average particle size is less than 1 nm,superparamagnetism occurs, and there is a risk that the amount ofmagnetic flux may decrease. On the other hand, if the average particlesize is larger than 20 nm, magnetic interaction is weakened, and it isnot preferable. In order to enhance the magnetic interaction between theparticles while maintaining a sufficient amount of magnetic flux, theparticle size is preferably in the range of from 1 nm to 20 nm, and morepreferably in the range of from 1 nm to 10 nm.

The metal nanoparticles 10 a may be either polycrystalline or singlecrystal, but the single crystal is preferred. In the case of singlecrystal metal nanoparticles, alignment of the axes of easy magnetizationis easily achieved, and magnetic anisotropy can be controlled.Therefore, the high frequency characteristics can be enhanced ascompared with the case of polycrystalline magnetic metal nanoparticles.

Furthermore, the metal nanoparticles 10 a may be spherical, but may alsobe flat-shaped or rod-shaped, both of which have large aspect ratios.Particularly, it is preferable that the average of the aspect ratio be 2or greater, and more preferably 5 or greater.

In the case of metal nanoparticles 10 a having a large aspect ratio, itis more preferable to coincide the long-side direction of individualmetal nanoparticles 10 a (in the case of a plate shape, the widthdirection; in the case of an oblate ellipsoid, the diameter direction;in the case of a rod shape, the rod length direction, and in the case ofan ellipsoid of revolution, the major axis direction) with the long-sidedirection of the magnetic particles (particle aggregates) 10 (in thecase of a plate shape, the width direction; in the case of an oblateellipsoid, the diameter direction; in the case of a rod shape, the rodlength direction, and in the case of an ellipsoid of revolution, themajor axis direction). Thereby, the directions of the axes of easymagnetization can be aligned into one direction, and the magneticpermeability and the high frequency characteristics of magneticpermeability can be enhanced.

The magnetic metal contained in the metal nanoparticles 10 a is the sameas the magnetic metal contained in the magnetic particles 10 describedabove. Since the description is redundant, the explanation of themagnetic metal will not be repeated here. It is preferable that themetal nanoparticles 10 a contain at least one non-magnetic metalselected from the group including Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn,Ba, Sr, Cr, Mo, Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn, and rare earthelements. These non-magnetic metals can enhance the electricalresistivity of the metal nanoparticles 10 a, and can enhance thermalstability and oxidation resistance, which is preferable. Among them, Aland Si are preferred because these elements can easily form solidsolutions with Fe, Co and Ni, which are used as the main component ofthe metal nanoparticles 10 a, and contribute to an enhancement of thethermal stability of the metal nanoparticles 10 a.

In regard to the amount of the non-magnetic metal, it is preferable thatthe metal nanoparticles contain the non-magnetic metal in an amount offrom 0.001 atom % to 20 atom % relative to the amount of the magneticmetal. If the respective contents of the non-magnetic metals exceed 20atom %, there is a risk that the saturation magnetization of themagnetic metal nanoparticles may be decreased. A more preferred amountfrom the viewpoints of high saturation magnetization and solidsolubilization is in the range of from 0.001 atom % to 5 atom %, andmore preferably in the range of from 0.01 atom % to 5 atom %.

At least a portion of the surfaces of the metal nanoparticles 10 a maybe covered with a coating layer. The coating layer is preferably formedfrom an oxide, a composite oxide, a nitride, a carbide or a fluoride,which contains at least one magnetic metal which is a constituentcomponent of the metal nanoparticles 10 a. When the coating layercontains at least one magnetic metal which is a constituent component ofthe metal nanoparticles 10 a, the adhesiveness between the metalnanoparticle 10 a and the coating layer increases, and thermal stabilityand oxidation resistance are enhanced.

Furthermore, the coating layer is more preferably formed from an oxide,a composite oxide, a nitride, a carbide or a fluoride, which contains atleast one non-magnetic metal selected from the group including Mg, Al,Si, Ca, Zr, Ti, Hf, Zn, Mn, Ba, Sr, Cr, Mo, Ag, Ga, Sc, V, Y, Nb, Pb,Cu, In, Sn, and rare earth elements. When the metal nanoparticles 10 acontain at least one non-magnetic metal selected from the groupincluding Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, Ba, Sr, Cr, Mo, Ag, Ga,Sc, V, Y, Nb, Pb, Cu, In, Sn, and rare earth elements, it is morepreferable that the coating layer be composed of an oxide, a compositeoxide, a nitride, a carbide or a fluoride, which contains at leastnon-magnetic metal that is the same as the non-magnetic metal which isone of the constituent components of the metal nanoparticles 10 a.Thereby, the adhesiveness between the metal nanoparticle 10 a and thecoating layer can be enhanced, and also, the thermal stability andoxidation resistance of the magnetic material can be enhanced.

Meanwhile, it is more preferable that the constitution of the coatinglayer as described above include an oxide or a composite oxide inparticular, among an oxide, a composite oxide, a nitride, a carbide or afluoride. This is because an oxide or a composite oxide is preferablefrom the viewpoints of the ease of the formation of a coating layer,oxidation resistance, and thermal stability.

Furthermore, the oxide or composite oxide coating layer is an oxide or acomposite oxide containing at least one of the magnetic metal which is aconstituent component of the metal nanoparticles 10 a, and is morepreferably an oxide or a composite oxide containing at least onenon-magnetic metal selected from the group including Mg, Al, Si, Ca, Zr,Ti, Hf, Zn, Mn, Ba, Sr, Cr, Mo, Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn,and rare earth elements.

This non-magnetic metal is an element which has small standard Gibbsenergy of formation of the oxide and is easily oxidized, and thenon-magnetic metal can easily form a stable oxide. The oxide coatinglayer that is formed from an oxide or a composite oxide containing atleast one or more of these non-magnetic metals can have enhancedadhesiveness and bindability to the metal nanoparticles 10 a, and canalso enhance the thermal stability and oxidation resistance of the metalnanoparticles 10 a.

Among the non-magnetic metals, Al and Si are preferred because theseelements can easily form solid solutions with Fe, Co and Ni, which areused as the main component of the magnetic metal particles, andcontribute to an enhancement of the thermal stability of the metalnanoparticles 10 a. A composite oxide which contains plural kinds ofnon-magnetic metals also encompasses a solid solution form. The coatinglayer that covers at least a portion of the surfaces of the metalnanoparticles 10 a not only enhances oxidation resistance of the metalnanoparticles 10 a in the interior, but also can enhance the electricalresistivity of the magnetic particles. By increasing the electricalresistivity, the eddy current loss at high frequencies can besuppressed, and the high frequency properties of magnetic permeabilitycan be improved. For this reason, the coating layer preferably has highelectrical resistivity, and for example, it is preferable that thecoating layer have an electrical resistivity of 1 mΩ·cm or higher.

As the coating layer is thicker, the electrical resistivity of themagnetic particles 10 increases, and the thermal stability and oxidationresistance of the metal nanoparticles 10 a also increase. However, ifthe coating layer is too thick, the magnetic interaction between themetal nanoparticles 10 a is easily broken, and individual metalnanoparticles 10 a are likely to behave magnetically independently. Thisis not preferable from the viewpoints of the magnetic permeability andthe high frequency properties of magnetic permeability. Furthermore,when the coating layer is thickened, the proportion of the magneticcomponents contained in the magnetic particles 10 decreases.Accordingly, the saturation magnetization of the magnetic particles 10is lowered, and the magnetic permeability is decreased, which is notpreferable. In order for the coating layer to have appropriately largeelectrical resistivity, to have individual metal nanoparticles 10 amagnetically bound, and to increase the saturation magnetization of themagnetic particles 10, it is more preferable that the coating layer havean average thickness of from 0.1 nm to 5 nm.

Meanwhile, in the current modification, the case in which theintermediate phase 10 b is present between the metal nanoparticles 10 awas described as an example; however, when the metal nanoparticles 10 ahas the coating layer described above, the coating layer can increasethe electrical resistivity between the metal nanoparticles 10 a, andalso the electrical resistivity of the magnetic particles 10. Therefore,it is also possible to employ a configuration in which the intermediatephase 10 b is omitted.

Also, it is preferable that the intermediate phase 10 b that is presentbetween the metal nanoparticles 10 a and contains at least onenon-magnetic metal selected from Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, Ba,Sr, Cr, Mo, Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn, and rare earthelements, and any one of oxygen (O), nitrogen (N) and carbon (C), have aelectrical resistivity of 1 mΩ·cm or higher.

These non-magnetic metals are elements which have small standard Gibbsenergy of formation of the oxide and are easily oxidized, and are metalsthat can easily form stable oxides, which is preferable. When the metal,semiconductor, oxide, nitride, carbide or fluoride, which contains sucha non-magnetic metal is present as the intermediate phase 10 b betweenthe metal nanoparticles 10 a, it is preferable because the electricalinsulation properties between the metal nanoparticles 10 a can befurther enhanced, and the thermal stability of the metal nanoparticlescan be enhanced.

Furthermore, it is preferable that the intermediate phase 10 b of ametal, a semiconductor, an oxide, a nitride, a carbide or a fluoridecontain at least one of the magnetic metals described, which arecontained in the metal nanoparticles 10 a. When the metal,semiconductor, oxide, nitride, carbide or fluoride contains at least oneof the metals that are the same as the magnetic metals contained in themetal nanoparticles 10 a, thermal stability and oxidation resistance areenhanced. Furthermore, when a ferromagnetic component is present betweenthe metal nanoparticles 10 a, the magnetic interaction between themagnetic metal nanoparticles is strengthened and the metal nanoparticles10 a and the intermediate phase 10 b can behave as aggregatesmagnetically. Thus, it is preferable from the viewpoint of enhancing themagnetic permeability and the high frequency properties of magneticpermeability.

Furthermore, similarly, when the intermediate phase 10 b of a metal, asemiconductor, an oxide, a nitride, a carbide or a fluoride contains atleast one of the same non-magnetic metals as the non-magnetic metalscontained in the metal nanoparticles 10 a, it is preferable becausethermal stability and oxidation resistance are enhanced.

Among the metal, semiconductor, oxide, nitride, carbide and fluoride, itis more preferable that the intermediate phase contain an oxide from theviewpoint of thermal stability.

Meanwhile, when the intermediate phase contains at least one magneticmetal and at least one non-magnetic metal that are contained in themetal nanoparticles, it is preferable that the atomic ratio of thenon-magnetic metal/magnetic metal in the intermediate phase be largerthan the atomic ratio of the non-magnetic metal/magnetic metal containedin the metal nanoparticles. This is because the metal nanoparticles canbe blocked with an “intermediate phase having a large ratio ofnon-magnetic metal/magnetic metal,” which has high oxidation resistanceand high thermal stability, and thus the oxidation resistance andthermal stability of the metal nanoparticles can be effectivelyincreased. Furthermore, it is preferable that the content of oxygencontained in the intermediate phase be larger than the content of oxygencontained in the metal nanoparticles. This is because the metalnanoparticles can be blocked with an “intermediate phase having a largeoxygen concentration and having high oxidation resistance and highthermal stability,” and the oxidation resistance and thermal stabilityof the metal nanoparticles can be effectively increased.

It is preferable that the intermediate phase 10 b of a metal, an oxide,a nitride, a carbide or a fluoride be composed of particles having asmaller particle size than the metal nanoparticles 10 a. At this time,the particles may be oxide particles, may be nitride particles, may becarbide particles, or may be fluoride particles. However, from theviewpoint of thermal stability, it is more preferable that theintermediate phase be composed of oxide particles. In the followingdescriptions, the case in which the intermediate phase 10 b be composedof oxide particles will be taken as an example in all cases.

Meanwhile, a more preferred state of existence of the oxide particles isa state in which the oxide particles are uniformly and homogeneouslydispersed between the metal nanoparticles 10 a. Thereby, more uniformmagnetic properties and dielectric properties can be expected. Theseoxide particles not only enhance the oxidation resistance and thesuppression of the aggregation of the metal nanoparticles 10 a, that is,thermal stability of the metal nanoparticles 10 a, but also electricallyseparate the metal nanoparticles 10 a. Thus, the oxide particles canincrease the electrical resistivity of the magnetic particles 10 and themagnetic material. When the electrical resistivity of the magneticmaterial is increased, the eddy current loss at high frequencies issuppressed, and the high frequency properties of magnetic permeabilitycan be enhanced. Accordingly, it is preferable that the oxide particleshave high electrical resistivity, and it is preferable that the oxideparticles have an electrical resistivity of 1 mΩ·cm or higher.

The oxide particles contains at least one non-magnetic metal selectedfrom the group including Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, Ba, Sr, Cr,Mo, Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn, and rare earth elements. Thesenon-magnetic metals are elements which have small standard Gibbs energyof formation of the oxide and are easily oxidized, and thesenon-magnetic metals can easily form stable oxides.

Further, when the metal nanoparticles 10 a include a coating layer, itis preferable that the ratio of non-magnetic metal/magnetic metal(atomic ratio) in these oxide particles be larger than the ratio ofnon-magnetic metal/magnetic metal (atomic ratio) in the coating layerthat covers the metal nanoparticles 10 a. As such, since the proportionof the non-magnetic metal is high, the oxide particles are thermallymore stable than the coating layer.

Accordingly, when such oxide particles are present in at least a portionof the space between the metal nanoparticles 10 a, the electricalinsulation properties between the metal nanoparticles 10 a can befurther enhanced, and the thermal stability of the magnetic metalnanoparticles can be enhanced.

Meanwhile, the oxide particles may not contain a magnetic metal, but itis more preferable that the oxide particles contain a magnetic metal. Apreferred amount of the magnetic metal that is contained in the oxideparticles is such that the proportion of the magnetic metal is 0.001atom % or more, and preferably 0.01 atom % or more, with respect to thenon-magnetic metal. This is because, if the oxide particles do notcontain a magnetic metal at all, the constituent components of thecoating layer that covers the surfaces of the metal nanoparticles 10 aand the oxide particles completely differ from each other, and it is notso preferable in view of adhesiveness or strength, and there is apossibility that thermal stability may be rather deteriorated. Also, ifthe oxide particles that are present between the metal nanoparticles donot contain a magnetic metal at all, it is difficult for the metalnanoparticles to magnetically interact with each other, and it is notpreferable from the viewpoints of the magnetic permeability and the highfrequency characteristics of magnetic permeability.

Therefore, more preferably, the oxide particles are a constituentcomponent of the metal nanoparticles 10 a, and it is preferable that theoxide particles contain at least one magnetic metal that is aconstituent component of the oxide coating layer, while it is morepreferable that the ratio of non-magnetic metal/magnetic metal (atomicratio) in the oxide particles be larger than the ratio of non-magneticmetal/magnetic metal (atomic ratio) in the oxide coating layer.

Meanwhile, the oxide particles are more preferably oxide particles thatcontain a non-magnetic metal that is of the same kind as thenon-magnetic metal contained in the metal nanoparticles 10 a, and of thesame kind as the non-magnetic metal contained in the oxide coatinglayer. It is because when the oxide particles are oxide particlescontaining a non-magnetic metal of the same kind, the thermal stabilityand oxidation resistance of the magnetic metal nanoparticles are furtherenhanced.

Meanwhile, the thermal stability enhancing effect, the electricalinsulation effect, and the adhesiveness and strength enhancing effect ofthe oxide particles as described above are exhibited particularly whenthe average particle size of the metal nanoparticles 10 a is small, andit is particularly effective when the particle size of the oxideparticles is smaller than the particle size of the metal nanoparticles10 a. Furthermore, the volume filling ratio of the metal nanoparticles10 a is preferably from 30 vol % to 80 vol % relative to the totalvolume of the magnetic particles 10 which are particle aggregates. Thevolume filling ratio is more preferably from 40 vol % to 80 vol %, andeven more preferably from 50 vol % to 80 vol %.

When the volume filling ratio of the metal nanoparticles 10 a isincreased, the distances between the metal nanoparticles 10 a that arecontained in the magnetic particles 10 are inevitably shortened.Therefore, the metal nanoparticles 10 a magnetically strongly interactwith each other, and behave as particle aggregates magnetically, so thatthe magnetic permeability can be increased. Since the metalnanoparticles 10 a are not physically perfectly connected, themicroscopic eddy current loss can be reduced, and the high frequencyproperties of magnetic permeability can be enhanced.

In order to exhibit this effect more effectively, the averageinterparticle distance of the metal nanoparticles 10 a contained in themagnetic particles 10 is preferably from 0.1 nm to 10 nm, and morepreferably from 0.1 nm to 5 nm. The interparticle distance as usedherein means the distance of the gap between two metal nanoparticles 10a, along a line connecting the center of one metal nanoparticle 10 a andthe center of another metal nanoparticle 10 a. When the surface of themetal nanoparticles 10 a is covered by a coating layer, theinterparticle distance refers to the distance of the gap between theoutermost surface of the surface coating layer of one metal nanoparticle10 a and the outermost surface of the surface coating layer of anothermetal nanoparticle 10 a.

When the interparticle distance is adjusted to a desired distance, themetal nanoparticles 10 a magnetically interact with each other, andbehave as particle aggregates (composite magnetic particles)magnetically, so that the magnetic permeability can be increased.Furthermore, since the metal nanoparticles 10 a are not physicallyperfectly connected, the microscopic eddy current loss can be reduced,and the high frequency properties of magnetic permeability can beenhanced.

In this specification, such a particle aggregate of the metalnanoparticles 10 a is regarded as one magnetic particle 10, but thereare occasions in which two or more particle aggregates join together inthe process of forming particle aggregates. Even in such cases, when aboundary line is drawn between particle aggregates, and the averageparticle size of one particle aggregate segregated by this boundary lineis from 50 nm to 50 μm, the segregated particle aggregate is acceptableas a particle aggregate, in the case of spherical aggregates.Furthermore, in the case of flat-shaped or rod-shaped particleaggregates, when the average height (in the case of a rod shape, theaverage diameter) is from 10 nm to 2 μm, and more preferably, when theaverage height is from 10 nm to 100 nm, and the aspect ratio is 5 orgreater, and more preferably 10 or greater, the segregated particleaggregate is acceptable as a particle aggregate.

Furthermore, there are also occasions in which a portion of one particleaggregate is bound to another particle aggregate. Even in this case,when a boundary line is drawn between the one particle aggregate and theportion of the other particle aggregate, if the conditions such asdescribed above are satisfied, the divided particle aggregate isacceptable as a particle aggregate having a shape in which a portion ofone particle aggregate is bound to another particle aggregate.

Furthermore, there are also occasions in which particle aggregateshaving a distorted shape other than a plate shape, an oblate ellipsoid,a rod shape, or an ellipsoid of revolution, are obtained. When the ratioof the long dimension and the short dimension, that is, the aspect ratiois 5 or greater, and more preferably 10 or greater, and the length(height) in the direction perpendicular to the longest diameter is from10 nm to 2 μm, and more preferably, the short dimension is from 10 nm to100 nm, the particle aggregate is acceptable as a particle aggregatehaving a distorted shape.

Furthermore, when a material other than the metal nanoparticles 10 a,which is contained in the particle aggregates, and the materialsurrounding the particle aggregates are the same, the outer periphery ofthe particle aggregates is ambiguous and not easily recognizable. Evenin such a case, if it can be confirmed by structural observation by TEMor SEM that the metal nanoparticles 10 a aggregate and segregate in acertain material, and particle aggregates are formed having an averageshort dimension of from 10 nm to 2 μm, and an average aspect ratio of 5or greater, the particle aggregate is acceptable as a particleaggregate. As discussed above, when the distance between the metalnanoparticles 10 a contained in the particle aggregates is 10 nm orless, the effect offered by the current modification is enhanced.Therefore, the distance between aggregated and unevenly distributedmetal nanoparticles is preferably 10 nm or less.

Furthermore, when a portion of one particle aggregate is bound toanother particle aggregate, and also in the case of a particle aggregatehaving a distorted shape other than a plate shape, an oblate ellipsoid,a rod shape, or an ellipsoid of revolution, if the height and aspectratio described above are satisfied when a boundary line is drawn, theparticle aggregate is acceptable as a particle aggregate. As one of themethods of drawing boundary lines, a method of drawing a boundary lineat a site where the average value of the interparticle distance betweenone metal nanoparticle 10 a and another metal nanoparticle 10 a presentin the vicinity is 10 nm or greater, and preferably 100 nm or greater,may be used.

Meanwhile, this is just one of possible methods after all, and inreality, it is preferable to determine, by structural observation by TEMor SEM to an extent based on common sense, a region in which there arerelatively more metal nanoparticles 10 a as compared with thesurroundings, and to draw a boundary line as one particle aggregate.Furthermore, it is preferable that the magnetic particles 10 have ashape with a large aspect ratio, from the viewpoints of high magneticpermeability and satisfactory high frequency magnetic properties.

Flat-shaped and rod-shaped magnetic particles are preferred, and theaverage height (in the case of a rod shape, the average diameter) ispreferably from 10 nm to 2 μm, more preferably from 10 nm to 2 μm, andeven more preferably from 10 nm to 100 nm. A larger average aspect ratiois more preferred, and an average aspect ratio of 5 or greater ispreferred. The average aspect ratio is more preferably 10 or greater.These are appropriate sizes for minimizing the sum of the eddy currentloss and the hysteresis loss in the MHz range of 100 kHz or higher.

Furthermore, a higher electrical resistivity of the magnetic particlesis more preferred; however, even if the intermediate phase 10 b of themetal, semiconductor, oxide, nitride, carbide or fluoride that iscontained in the magnetic particles 10 has higher resistivity, generallyas the volume proportion of the metal nanoparticles 10 a increases, theelectrical resistivity of the magnetic particles 10 decreases. This isbecause in reality, the metal nanoparticles 10 a do not isolatethemselves, but partially form a network or aggregate. Such an effectbecomes conspicuous as the particle size of the metal nanoparticles 10 ais smaller, and the volume proportion is larger.

On the other hand, if the volume ratio of the metal nanoparticles 10 ais decreased, the content of the magnetic component contained in themagnetic particles 10 decreases. Therefore, a decrease in the saturationmagnetization is caused, and it is not preferable. As such, theelectrical resistivity and saturation magnetization of the magneticparticles 10 are in a trade-off relationship to some extent.

Ideally, when the volume ratio of the metal nanoparticles in themagnetic particles is from 30 vol % to 80 vol %, more preferably from 40vol % to 80 vol %, and even more preferably from 50 vol % to 80 vol %,it is preferable if the electrical resistivity of the magnetic particles10 can be maximized. The electrical resistivity is preferably from 100μΩ·cm to 100 mΩ·cm.

That is, a preferred range of electrical resistivity in which a balanceis achieved between high saturation magnetization and high electricalresistivity is from 100 μΩ·cm to 100 mΩ·cm. Meanwhile, such magneticparticles 10 are capable of inducing in-plane uniaxial anisotropy bymeans of the magnetic field or strain, which is preferable. As discussedabove, in a magnetic material having in-plane uniaxial anisotropy, theanisotropic magnetic field in an easy magnetization plane is preferablyfrom 1 Oe to 500 Oe, and more preferably from 10 Oe to 500 Oe. This isan appropriate range to maintain low loss and high magnetic permeabilityin the MHz range of 100 kHz or higher.

The composition of the magnetic particles 10 or the like can be easilyanalyzed by using a transmission electron microscope-energy dispersiveX-ray spectrometer (TEM-EDX). According to the TEM-EDX, the approximatecomposition of the particles can be checked by irradiating the particleswith EDX and determining the composition semi-quantitatively. At thistime, even the approximate composition of nanoparticles can be checkedby narrowing the beam diameter. Also, techniques such as inductivelycoupled plasma (ICP) atomic emission spectrometry, X-ray photoelectronspectroscopy (XPS), and secondary ion mass spectrometry (SIMS) can alsobe utilized. According to ICP atomic emission spectrometry, thecomposition of metals and oxides can be quantitatively determined byselecting the types of acids and alkalis for dissolving the components.That is, a metal dissolved in a weak acid, and an oxide dissolved in analkali or a strong acid can be separated and quantified. Furthermore,according to XPS, the binding state of various elements that constitutethe particles can be investigated.

The average particle size of the magnetic particles 10 can be determinedby TEM observation or SEM observation, and in the case where theparticles are spherical, the average particle size can be determined bydefining the average of the longest diagonal and the shortest diagonalof individual particles as the particle diameters, and calculating theaverage of the particle diameters of plural particles, for example, 50particles. Meanwhile, when the average particle size of the magneticparticles is as small as 50 nm or less, and it is difficult todistinguish the particle size by TEM, the crystal grain size that can bedetermined by X-ray diffraction (XRD) measurement can be used as asubstitute. That is, for the maximum peak among the peaks attributableto the magnetic particles, the crystal grain size can be determined byXRD using Scherrer's formula from the diffraction angle and thehalf-width. Scherer's formula is represented by D=0.9λ/(β cos θ),wherein D represents the crystal grain size, λ represents the wavelengthof the X-ray for measurement, β represents the half-width, and θrepresents Bragg diffraction angle. Even for flat-shaped or rod-shapedparticles having large aspect ratios, the respective long dimensions (inthe case of a flat shape, the diameter; and in the case of a rod shape,the length of the rod), or the respective short dimensions (in the caseof a flat shape, the height; and in the case of a rod shape, thediameter of the bottom surface of the rod) can be determined by the sametechnique. The aspect ratio is determined by analyze an image by TEM orSEM to analyze plural magnetic particles, and calculating the averagevalue. Furthermore, the volume ratio or the volume filling ratio of themagnetic particles can be simply calculated by making TEM observation orSEM observation, and determining the average particle size, the averageaspect ratio, and the number proportion.

Whether the magnetic metal and the non-magnetic metal contained in themagnetic particles 10 form a solid solution can be determined from thelattice constant measured by XRD. For example, when Fe as a magneticmetal and Al as a non-magnetic metal, which are contained in themagnetic particles 10, form a solid solution, the lattice constant of Fevaries with the amount of solid solution. In the case of bcc-Fe in whichno solid solution is formed, the lattice constant is ideallyapproximately 2.86. However, when Fe and Al form a solid solution, thelattice constant increases, and a solid solution of about 5 atom % of Alincreases the lattice constant by about 0.005 to 0.01. In a solidsolution of about 10 atom % of Al, the lattice constant increases byabout 0.01 to 0.02. As such, by performing an XRD measurement of themagnetic particles 10, the lattice constant of the magnetic metal can bedetermined, and based on the magnitude, it can be easily determinedwhether the metals have formed a solid solution, and to what extent thesolid solution has been formed. Furthermore, whether a solid solutionhas been formed can be confirmed from a diffraction pattern of theparticles by TEM or a high resolution TEM photograph. In addition, thecrystal structure of the magnetic metal is slightly distorted when theparticle size of the magnetic particles 10 decreases, and particularlywhen the particle size is in the nanometer order. Also, the crystalstructure is also slightly distorted when a core-shell structurecomposed of a magnetic particle 10 and a coating layer is adopted. Thisis because when the size of the magnetic metal at the core decreases ora core-shell structure is adopted, strain occurs at the interface of thecore and the shell. In regard to the lattice constant, it is necessaryto comprehensively determine the value in consideration of such effects.

FIG. 3 is a schematic diagram of a second modification of the currentembodiment. The magnetic material is the same as the magnetic materialillustrated in FIG. 1, except that a second coating layer 18 of a thirdoxide which coats at least a portion of a magnetic particle 10 andcontains at least one each of the magnetic metals and the non-magneticmetals contained in the magnetic particle 10 is included between themagnetic particle 10 and the coating layer 12.

As illustrated in FIG. 3, it is preferable that the magnetic particles10 have at least a portion of the surfaces covered by a third oxidecontaining at least one each of the non-magnetic metals and the magneticmetals which are the constituent components of the magnetic particles10. It is because when a portion of the surfaces of the magneticparticles 10 is covered by a third oxide, the aggregation of themagnetic particles 10 can be effectively suppressed.

At this time, when the third oxide contains at least one each of thenon-magnetic metals and the magnetic metals which are the constituentcomponents of the magnetic particles 10, the adhesiveness between themagnetic particle 10 and the second coating layer 18 can bestrengthened. Thus, high strength, high thermal stability, and highoxidation resistance characteristics can be realized while theaggregation of the magnetic particles 10 is suppressed.

Meanwhile, at this time, it is preferable that the first oxide describedabove and the third oxide, and the second oxide described above and thethird oxide be respectively a combination that does not have an eutecticpoint at or below 1000° C. Thereby, the aggregation of the magneticparticles is suppressed even in a high temperature environment, and thethermal stability can be enhanced. Furthermore, the proportion of thenon-magnetic metal/magnetic metal contained in the third oxide ispreferably larger than the proportion of the non-magnetic metal/magneticmetal contained in the magnetic particles 10. Thereby, the oxidationresistance and thermal stability of the magnetic particles 10 can beeffectively increased by employing the third oxide.

Furthermore, the magnetic material of the current embodiment preferablycontains intermediate particles. These intermediate particles areparticles of an oxide, a nitride, a carbide or a fluoride, whichcontains at least one non-magnetic metal selected from Mg, Al, Si, Ca,Zr, Ti, Hf, Zn, Mn, rare earth elements, Ba, and Sr, and the particlespreferably have a resistivity of 1 mΩ·cm or higher.

Furthermore, these intermediate particles may have the same compositionas that of the third oxide, if the second coating layer 18 is provided.The intermediate particles have an average particle size of from 1 nm to100 nm, and it is preferable that the average particle size of theintermediate particles be smaller than the average particle size of themagnetic particles 10. Such intermediate particles are preferablebecause the intermediate particles can further enhance the electricalinsulation properties between the magnetic particles by existing betweenthe magnetic particles, and also can enhance thermal stability of themagnetic particles.

The three components of the third oxide, the eutectic structure and theintermediate particles are desirably such that the total volume of thethree components is from 10 vol % to 90 vol % relative to the volume ofthe entirety of the magnetic material. When the total volume is in sucha range, the electrical insulation properties of the magnetic materialare enhanced, the eddy current loss is effectively suppressed, and thehigh frequency magnetic properties can be enhanced. Furthermore, thethermal stability and oxidation resistance of the magnetic particles canalso be effectively enhanced, and thus it is desirable.

Furthermore, the magnetic material of the current embodiment may includevoids, but since voids decrease the volume fraction of the magneticparticles 10 and also deteriorate the strength, thermal stability, andoxidation resistance of the magnetic material. Thus, voids are not verypreferable. Therefore, it is preferable that there be as fewer voids aspossible.

In the current embodiment, it is preferable that the third oxide, theeutectic structure and the intermediate particles all have highelectrical resistivity, and for example, they preferably have anelectrical resistivity of 1 mΩ·cm or higher. Thereby, the electricalresistivity of the magnetic material can be increased, and the eddycurrent loss can be effectively suppressed.

Furthermore, the second coating layer 18 of the third oxide is such thatas the second coating layer is thicker, the electrical resistivity ofthe magnetic material increases, and the thermal stability and oxidationresistance of the magnetic particles are also enhanced. However, if thesecond coating layer 18 is made too thick, the volume fraction of themagnetic particles decreases, and saturation magnetization is alsodecreased, which is not preferable. Also, a thick second coating layercauses a decrease in the magnetic permeability, and it is notpreferable. For this reason, it is more preferable that the secondcoating layer 18 have an average thickness of from 0.1 nm to 5 nm.

The composition analysis of the third oxide, the eutectic structureformed from the first oxide and the second oxide, and the intermediateparticles can be easily carried out by techniques such as TEM-EDX, XPS,and SIMS, similarly to the analysis of the magnetic particles asdescribed above. Particularly, when TEM-EDX is used, the composition ofeach of the structures can be easily checked by irradiating EDX to eachstructure by adjusting the beam, and determining the composition in asemi-quantitative manner. Also, the size or volume proportion of thefirst oxide, the second oxide, the eutectic structure and theintermediate particles can be determined by a TEM-EDX analysis or aSEM-EDX analysis, and the volume proportion can be simply calculated bymaking a TEM observation or a SEM observation, and performing an imageanalysis.

Examples of morphologies of the magnetic material of the currentembodiment include a bulk form (a pellet shape, a ring shape, arectangular shape, or the like), a film form including sheets, and apowder form.

By having configurations such as described above, the magnetic materialof the current embodiment has a high real part of the magneticpermeability (μ′) and a low imaginary part of the magnetic permeability(μ″) in the MHz range of 100 kHz or higher, and can realize highstrength, high saturation magnetization, high thermal stability and highoxidation resistance.

Second Embodiment

The magnetic material of the current embodiment includes magneticparticles containing at least one magnetic metal selected from the groupincluding Fe, Co and Ni, and at least one non-magnetic metal selectedfrom Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, rare earth elements, Ba and Sr;a first coating layer of a first oxide that covers at least a portion ofthe magnetic particles; and oxide particles of a second oxide that arepresent between the magnetic particles and constitute an eutecticreaction system with the first oxide.

The second embodiment is the same as the first embodiment, except thatan oxide phase containing an eutectic structure of the first oxide andthe second oxide is not present. Therefore, further descriptions on thematters that overlap with the first embodiment will not be repeated.

FIG. 4 is a schematic diagram of the magnetic material of the currentembodiment. The magnetic material of the current embodiment is composedof magnetic particles 10, a first coating layer 12 of a first oxide thatcover these magnetic particles 10, and oxide particles 14 of a secondoxide that are present between the magnetic particles 10.

The first oxide and the second oxide constitute an eutectic reactionsystem. That is, the first oxide and the second oxide produce eutecticcrystals. The first oxide is, for example, an oxide of Si (silicon), andthe second oxide is, for example, an oxide of B (boron).

The magnetic material of the current embodiment is a so-called precursorfor producing the magnetic material of the first embodiment. When themagnetic material of the current embodiment is used, the magneticmaterial of the first embodiment can be easily produced.

Furthermore, the magnetic material of the current embodiment realizeshigh magnetic permeability, low loss, and high saturation magnetizationin the MHz range of 100 kHz or higher, by having the configurationdescribed above.

Meanwhile, the space between the magnetic particles 10 and the oxideparticles 14 may be, for example, hollow, or may be filled with a resinor the like.

Third Embodiment

The method for producing a magnetic material of the current embodimentincludes a step of synthesizing magnetic particles containing at leastone magnetic metal selected from the group including Fe, Co and Ni, andat least one non-magnetic metal selected from Mg, Al, Si, Ca, Zr, Ti,Hf, Zn, Mn, rare earth elements, Ba and Sr; a step of forming a firstcoating layer of a first oxide that covers at least a portion of themagnetic particles; and a step of mixing oxide particles of a secondoxide that constitutes an eutectic reaction system with the first oxide,with the magnetic particles.

The method for producing a magnetic material of the current embodimentis a method for producing the magnetic material of the secondembodiment. Therefore, further descriptions on the matters that overlapwith the second embodiment will not be repeated.

First, the production method includes a step of synthesizing magneticparticles containing at least one magnetic metal selected from the groupincluding Fe, Co and Ni, and at least one non-magnetic metal selectedfrom Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, rare earth elements, Ba and Sr.At this time, the step of synthesizing magnetic particles is notparticularly limited, and the synthesis is carried out by, for example,a water atomization method, a gas atomization method, a heat plasmamethod, a CVD method, a laser abrasion method, an in-liquid dispersionmethod, or the like.

Meanwhile, as disclosed in the first modification of the firstembodiment, in the case of synthesizing particle aggregates including,as magnetic particles, metal nanoparticles that have an average particlesize of from 1 nm to 20 nm and contain at least one magnetic metalselected from the group including Fe, Co and Ni; and an intermediatephase that is present between the metal nanoparticles, and contains ametal, a semiconductor, an oxide, a nitride, a carbide or a fluoride,which contains at least one non-magnetic metal selected from Mg, Al, Si,Ca, Zr, Ti, Hf, Zn, Mn, Ba, Sr, Cr, Mo, Ag, Ga, Sc, V, Y, Nb, Pb, Cu,In, Sn, and rare earth elements, and at least one magnetic metalmentioned above, it is preferable to select a method such as describedbelow.

That is, first, a magnetic metal powder having an average particle sizeof several micrometers and a non-magnetic metal powder, which are rawmaterials, are sprayed together with a carrier gas into a plasmagenerated in a chamber of a high frequency induction heat plasmaapparatus. Thereby, magnetic metal nanoparticles having a size in thenanometer order can be synthesized.

At this time, metal nanoparticles having the surfaces coated with anon-magnetic metal oxide can be synthesized by appropriately controllingthe synthesis conditions, and thus, it is preferable. That is, it ispreferable because a two-phase separated structure of metals and oxidesat a nanoscale level can be realized.

Thereafter, magnetic particles that are obtained by rapidly cooling thesynthesis product are subjected to a composite integration treatment byusing a high-power mill apparatus. Thereby, the particle aggregatesdescribed above can be obtained relatively easily.

The high-power mill apparatus is not limited in the selection of thetype, as long as it is an apparatus capable of applying stronggravitational acceleration, but for example, a high-power planetary millapparatus which is capable of applying a gravitational acceleration ofseveral ten G's, or the like is preferred. If possible, it is preferableto apply a gravitational acceleration of 50 G or greater, and morepreferably 100 G or greater.

Furthermore, when a high-power mill apparatus is used, it is preferableto perform the process in an inert gas atmosphere in order to suppressoxidation of the metal nanoparticles as much as possible. Also, if apowder is subjected to a composite integration treatment in a dry mode,the composite integration treatment can be easily carried out; however,the structure is likely to become coarse, and collection of theparticles is difficult. In order to suppress coarsening of thestructure, a wet type composite integration treatment using a liquidsolvent is preferred. A more preferred method is to perform a treatmentof suppressing the coarsening of the structure, while acceleratingcomposite integration, by carrying out the treatment both in a dry modeand in a wet mode.

By using such a method, particle aggregates can be easily synthesized asmagnetic particles. Depending on the synthesis conditions, shaping theparticle aggregates into a flat shape with a large aspect ratio can bereadily realized, and thus, it is preferable. When the particleaggregates are prepared into composite particles having a large aspectratio, shape-induced magnetic anisotropy can be imparted, and as thedirections of the axes of easy magnetization are aligned into onedirection, the magnetic permeability and the high frequency propertiesof magnetic permeability can be enhanced, which is preferable.Meanwhile, even if the particles undergo slight oxidation, the particlescan be reduced by subjecting the particles to a heat treatment in areducing atmosphere.

Furthermore, as disclosed in the second modification of the firstembodiment, when the magnetic particles are synthesized, it ispreferable to synthesize magnetic particles in which at least a portionof the surface is covered with a third oxide. In this case, the methodof forming a coating layer of the third oxide (second coating layer) isnot particularly limited, but examples include methods based on liquidphase coating or partial oxidation.

A partial oxidation method is a method of synthesizing magneticparticles containing a magnetic metal and a non-magnetic metal,subsequently subjecting the magnetic particles to partial oxidationunder appropriate oxidation conditions, and thereby precipitating anoxide containing the non-magnetic metal on the surface of the magneticparticles to form a coating layer. This technique is based on causingthe precipitation of an oxide through diffusion, and when compared witha liquid phase coating method, the magnetic particles and the interfacebetween the magnetic particles and the oxide coating layer stronglyadhere to each other, so that the thermal stability and oxidationresistance of the magnetic particles are enhanced, which is preferable.There are no particular limitations on the conditions for partialoxidation, but it is preferable to oxidize the magnetic particles in anoxidative atmosphere of O₂, CO₂ or the like, at an adjusted oxygenconcentration and at a temperature in the range of room temperature to1,000° C.

Next, a coating layer of a first oxide (first coating layer) is formedon at least a portion of the surfaces of the magnetic particles thussynthesized. In the present step, there are no particular limitations onthe technique of forming the first coating layer of the first oxide, butexamples include a CVD method and an in-liquid sol-gel method inparticular.

Next, the oxide particles of the second oxide that constitutes aneutectic reaction system with the first oxide are mixed with themagnetic particles. The present step is a step of mixing two kinds ofparticles, and as long as uniform mixing can be achieved, the method ofmixing is not particularly limited. For example, mixing can be achievedby using a rotary ball mill, a vibratory ball mill, a stirring ballmill, a planetary mill, a jet mill, and mortar mixing. In all cases, itis desirable that the magnetic particles including the first coatinglayer of the first oxide and the oxide particles of the second oxide beuniformly mixed.

Meanwhile, after each process, it is desirable to control the variousprocess conditions, so as to prevent the magnetic particles from beingoxidized, and to prevent a reduction in the saturation magnetization.Depending on the cases, magnetic particles that have undergone oxidationand a reduction in the saturation magnetization may be reduced, and thesaturation magnetization may be restored, after each process. In regardto the conditions for reducing, it is preferable to subject the magneticparticles to a heat treatment at a temperature in the range of 100° C.to 1,000° C. in a reducing atmosphere of H₂, CO, CH₄ or the like. Atthis time, it is preferable to select conditions in which aggregationand necking of the magnetic particles can hardly occur.

Examples of morphologies of the magnetic material include a bulk form (apellet shape, a ring shape, a rectangular shape, or the like), a filmform including sheets, and a powder. There are no particular limitationson the technique of making the magnetic material in a bulk form, butuniaxial press molding, hot press molding, cold isostatic pressing(CIP), hot isostatic pressing (HIP), spark plasma sintering (SPS), andthe like may be used. Particularly, in the case of molding whileheating, such as in the case of hot press molding, HIP, and SPS, it ispreferable to carry out the process in an atmosphere at a low oxygenconcentration. A vacuum atmosphere, or a reducing atmosphere of H₂, CO,CH₄ or the like is preferred. This is to prevent the magnetic particlesfrom being oxidized and deteriorating during the molding under heating.

Furthermore, there are no particular limitations on the method ofproducing a sheet, but for example, a sheet can be produced by mixingthe mixed particles of magnetic particles and oxide particles thussynthesized, with a resin and a solvent to prepare a slurry, andapplying and drying the slurry. Furthermore, a mixture of the mixedparticles and a resin may also be pressed to be molded into a sheet formor a pellet form.

Furthermore, the mixed particles may also be dispersed in a solvent anddeposited by an electrophoresis method or the like. When produced into asheet, it is desirable to orient the mixed particles into one direction,that is, a direction in which the easy axes of individual magneticparticles are gathered. It is preferable because thereby, the magneticpermeability and the high frequency properties of magnetic permeabilityof the magnetic material sheet in which the magnetic particles have beenassembled can be enhanced. Examples of techniques for orienting theparticles include application and drying of the dispersion in a magneticfield, but there are no particular limitations on the technique.

A magnetic sheet may be formed into a laminate structure. When the sheetis formed into a laminate structure, the sheet can be easily thickened,and also, the high-frequency magnetic properties can be enhanced byalternately laminating the magnetic sheet with a non-magnetic insulatinglayer. That is, when a magnetic layer containing magnetic particles isformed into a sheet form having a thickness of 100 μm or less, thissheet-like magnetic layer is alternately laminated with a non-magneticinsulating oxide layer having a thickness of 100 μm or less to obtain alaminate structure, the high-frequency magnetic properties are enhanced.That is, by adjusting the thickness of a single magnetic layer to 100 μmor less, the effect of a demagnetizing field can be reduced when ahigh-frequency magnetic field is applied in the in-plane direction, sothat not only the magnetic permeability can be increased, but also thehigh frequency properties of magnetic permeability are enhanced. Thereare no particular limitations on the method of lamination, butlamination can be carried out by stacking plural sheets of magneticsheets, and pressing the sheets by a pressing method or the like, orheating and sintering the sheets.

The magnetic material produced by a production method such as describedabove has a high real part of magnetic permeability (μ′) and a lowimaginary part of magnetic permeability (μ″) in the MHz range of 100 kHzor higher, and also has high strength, high saturation magnetization,high thermal stability, and high oxidation resistance. Furthermore, themagnetic material can also be used as a precursor for producing amagnetic material having such properties.

Fourth Embodiment

The method for producing a magnetic material of the current embodimentincludes a step of synthesizing magnetic particles containing at leastone magnetic metal selected from the group including Fe, Co and Ni, andat least one non-magnetic metal selected from Mg, Al, Si, Ca, Zr, Ti,Hf, Zn, Mn, rare earth elements, Ba and Sr; a step of forming a firstcoating layer of a first oxide that covers at least a portion of themagnetic particles; a step of mixing oxide particles of a second oxidethat constitutes an eutectic reaction system with the first oxide, withthe magnetic particles; and a step of subjecting the first coating layerand the oxide particles to eutectic melting and solidification by a heattreatment at or below 1,000° C. and cooling.

The method for producing a magnetic material of the current embodimentis a method for producing the magnetic material of the third embodiment.Therefore, further descriptions on the matters that overlap with thethird embodiment will not be repeated. Furthermore, the productionmethod is the same as the method for producing a magnetic material asdescribed in the third embodiment, except that a step of subjecting thefirst coating layer and the oxide particles to eutectic melting andsolidification by a heat treatment at or below 1,000° C. and cooling isincluded. Therefore, further descriptions on the matters that overlapwith the third embodiment will not be repeated.

In the method for producing a magnetic material of the currentembodiment includes a step of subjecting the mixed particles of magneticparticles having a first coating layer of a first oxide and oxideparticles of a second oxide as produced in the third embodiment, to aheat treatment at a temperature of 1,000° C. or lower and cooling, tothereby subjecting the first coating layer and the oxide particles toeutectic melting and solidification. At this time, the heat treatmentconditions are selected such that a portion of the first coating layerand a portion of the oxide particles remain unreacted.

The atmosphere for the heat treatment is preferably a vacuum atmosphere,or a reducing atmosphere of H₂, CO, CH₄ or the like. This is to preventthe magnetic particles from being oxidized and deteriorating during themolding under heating. Furthermore, in order to suppress aggregation andnecking of the magnetic particles as much as possible, a lower heattreatment temperature is preferred. It is preferable to melt themagnetic particles at a temperature near the eutectic point of the firstoxide and the second oxide. Therefore, it is preferable to select acombination of compositions having a low eutectic point of the firstoxide and the second oxide.

The magnetic material produced by the production method such asdescribed above has a high real part of magnetic permeability (μ′) and alow imaginary part of magnetic permeability (μ″) in the MHz range of 100kHz or higher, and has high strength, high saturation magnetization,high thermal stability, and high oxidation resistance.

Fifth Embodiment

The magnetic material of the current embodiment includes magneticparticles which contain at least one magnetic metal selected from thegroup including Fe, Co and Ni, and at least one non-magnetic metalselected from Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, Ba, Sr, Cr, Mo, Ag,Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn, and rare earth elements, and areparticle aggregates having plural metal nanoparticles that have anaverage particle size of from 1 nm to 20 nm and contain at least onemagnetic metal selected from the group including Fe, Co and Ni, andhaving a morphology with an average short dimension of from 10 nm to 2μm and an average aspect ratio of 5 or greater; and an oxide phase thatis present between the magnetic particles and has an eutectic structureof a first oxide and a second oxide that constitute an eutectic reactionsystem.

The current embodiment is the same as the first modification of thefirst embodiment, except that the magnetic material does not have thefirst coating layer 12 and the oxide particles 16 illustrated in FIG. 2.Therefore, further descriptions on any overlapping matters will not berepeated here.

FIG. 5 is a schematic diagram of the magnetic material of the currentembodiment. The magnetic particles 10 includes an intermediate phase 10b that is present between metal nanoparticles 10 a, and contains atleast one non-magnetic metal selected from Mg, Al, Si, Ca, Zr, Ti, Hf,Zn, Mn, Ba, Sr, Cr, Mo, Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn, and rareearth elements, and any one of oxygen (O), nitrogen (N) and carbon (C).The intermediate phase 10 b may also contain fluorine (F). Theintermediate phase 10 b is, for example, a metal, a semiconductor, anoxide, a nitride, a carbide, or a fluoride. Furthermore, theintermediate phase 10 b has higher resistance than the magneticparticles 10.

The magnetic particles 10 are particle aggregates of the metalnanoparticles 10 a having a morphology with an average short dimensionof from 10 nm to 100 nm and an average aspect ratio of 10 or greater,and the intermediate phase 10 b, and the volume filling ratio of themetal nanoparticles 10 a is from 40 vol % to 80 vol % relative to thetotal volume of the particle aggregates. Such particle aggregates arealso referred to as nanogranular type magnetic particles.

The magnetic material of FIG. 5 has a structure in which theintermediate phase 10 b fills in between the metal nanoparticles 10 a.

The magnetic material of the current embodiment realizes high magneticpermeability and low loss in the MHz range of 100 kHz or higher, byhaving the configuration described above. Furthermore, the magneticmaterial can also realize high saturation magnetization, high thermalstability, and high oxidation resistance.

Sixth Embodiment

The magnetic material of the current embodiment includes magneticparticles containing at least one magnetic metal selected from the groupincluding Fe, Co and Ni, and at least one non-magnetic metal selectedfrom Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, rare earth elements, Ba and Sr;a second coating layer of a third oxide that covers at least a portionof the magnetic particles, and contains at least one each of themagnetic metals described above and the non-magnetic metals describedabove; and an oxide phase that is present between the magneticparticles, and has an eutectic structure of the first oxide and thesecond oxide constituting an eutectic reaction system.

The current embodiment is the same as the second modification of thefirst embodiment, except that the magnetic material does not have thefirst coating layer 12 and the oxide particles 16 illustrated in FIG. 3.Therefore, further descriptions on any overlapping matters will not berepeated here.

FIG. 6 is a schematic diagram of the magnetic material of the currentembodiment. The magnetic material includes magnetic particles 10containing at least one magnetic metal selected from the group includingFe, Co and Ni, and at least one non-magnetic metal selected from Mg, Al,Si, Ca, Zr, Ti, Hf, Zn, Mn, rare earth elements, Ba and Sr; a secondcoating layer 18 of a third oxide that covers at least a portion of themagnetic particles 10, and contains at least one each of the magneticmetals described above and the non-magnetic metals described above; andan oxide phase 16 that is present between the magnetic particles 10, andhas an eutectic structure of the first oxide and the second oxideconstituting an eutectic reaction system.

The magnetic material of the current embodiment realizes high magneticpermeability and low loss in the MHz range of 100 kHz or higher, byhaving the configuration described above. Furthermore, the magneticmaterial can also realize high saturation magnetization, high thermalstability, and high oxidation resistance.

Seventh Embodiment

The magnetic material of the current embodiment includes magneticparticles which are particle aggregates containing metal nanoparticlesthat have an average particle size of from 1 nm to 10 nm, contain atleast one magnetic metal selected from the group including Fe, Co andNi, and also containing an intermediate phase of a metal, asemiconductor, an oxide, a nitride, a carbide or a fluoride, which ispresent between the metal nanoparticles and contains at least onenon-magnetic metal selected from Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, Ba,Sr, Cr, Mo, Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn, and rare earthelements and at least one magnetic metal described above, and have amorphology with an average short dimension of from 10 nm to 100 nm andan average aspect ratio of 10 or greater, in which the volume fillingratio of the metal nanoparticles is from 40 vol % to 80 vol % relativeto the total volume of the particle aggregates.

In the magnetic material of the current embodiment, the averageinterparticle distance between the metal nanoparticles is morepreferably from 0.1 nm to 5 nm.

FIG. 7 is a schematic diagram of the magnetic material of the currentembodiment. The magnetic material of the current embodiment includesplural magnetic particles 10. The magnetic particle 10 includes metalnanoparticles 10 a and an intermediate phase 10 b. The metalnanoparticles 10 a has an average particle size of from 1 nm to 20 nm,and more preferably of from 1 nm to 10 nm. The metal nanoparticles 10 acontain at least one magnetic metal selected from the group includingFe, Co and Ni. The intermediate phase 10 b that is present between themetal nanoparticles 10 a, contains at least one non-magnetic metalselected from Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, Ba, Sr, Cr, Mo, Ag,Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn, and rare earth elements, and any oneof oxygen (O), nitrogen (N) and carbon (C). The intermediate phase 10 bmay also contain fluorine (F). The intermediate phase 10 b is, forexample, a metal, a semiconductor, an oxide, a nitride, a carbide, or afluoride. Furthermore, the intermediate phase 10 b has higher electricalresistivity than the magnetic particles 10.

Furthermore, the magnetic particles 10 are particle aggregates of themetal nanoparticles 10 a having a morphology with an average shortdimension of from 10 nm to 2 μm (more preferably of from 10 nm to 100nm) and an average aspect ratio of 5 or greater (more preferably of from10 or greater), and the intermediate phase 10 b, and the volume fillingratio of the metal nanoparticles 10 a is from 40 vol % to 80 vol %relative to the total volume of the particle aggregates. Such particleaggregates are also referred to as nanogranular type magnetic particles.

The magnetic material of FIG. 7 has a structure in which theintermediate phase 10 b fills in between the metal nanoparticles 10 a.

In such particle aggregates, the metal nanoparticles 10 a are likely tobe magnetically bound to each other, and behave as one aggregatemagnetically. On the other hand, since the intermediate phase 10 bhaving high electrical resistivity, for example, an oxide, is presentbetween the metal nanoparticles 10 a, the electrical resistivity of themagnetic particles 10 can be made large. Therefore, the eddy currentloss can be suppressed while high magnetic permeability is maintained,and thus it is preferable.

The metal nanoparticles 10 a have an average particle size of from 1 nmto 20 nm, and more preferably of from 1 nm to 10 nm. If the averageparticle size is less than 1 nm, superparamagnetism occurs, and there isa risk that the amount of magnetic flux may decrease. On the other hand,if the average particle size is larger than 10 nm, magnetic bindabilityis weakened, and it is not preferable. A preferred range of particlesize in order to enhance the magnetic interaction between the particleswhile maintaining a sufficient amount of magnetic flux is from 1 nm to20 nm, and more preferably of from 1 nm to 10 nm.

The metal nanoparticles 10 a may be polycrystalline or may be singlecrystal, but a single crystal is preferred. In the case of metalnanoparticles of single crystal, it is easy to align the axes of easymagnetization, and magnetic anisotropy can be controlled. For thisreason, the high frequency properties can be enhanced as compared withthe case of polycrystalline magnetic metal nanoparticles.

Furthermore, the metal nanoparticles 10 a may be spherical in shape, buta flat shape or a rod shape, both of which have large aspect ratios, mayalso be used. Particularly, the average of the aspect ratio is desirably2 or greater, and more preferably 5 or greater.

In the case of metal nanoparticles 10 a having a large aspect ratio, itis more preferable to coincide the long-side direction of individualmetal nanoparticles 10 a (in the case of a plate shape, the widthdirection; in the case of an oblate ellipsoid, the diameter direction;in the case of a rod shape, the rod length direction, and in the case ofan ellipsoid of revolution, the major axis direction) with the long-sidedirection of the magnetic particles (particle aggregates) 10 (in thecase of a plate shape, the width direction; in the case of an oblateellipsoid, the diameter direction; in the case of a rod shape, the rodlength direction, and in the case of an ellipsoid of revolution, themajor axis direction). Thereby, the directions of the axes of easymagnetization can be aligned into one direction, and the magneticpermeability and the high frequency properties of magnetic permeabilitycan be enhanced.

The metal nanoparticles 10 a contain at least one magnetic metalselected from the group including Fe (iron), Co (cobalt) and Ni(nickel). The metal nanoparticles 10 a preferably contain at least onenon-magnetic metal selected from the group including Mg, Al, Si, Ca, Zr,Ti, Hf, Zn, Mn, Ba, Sr, Cr, Mo, Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn,and rare earth elements. These non-magnetic metals can enhance theresistance of the metal nanoparticles 10 a, and can enhance thermalstability and oxidation resistance, which is preferable. Among them, Aland Si are preferred because these elements can easily form solidsolutions with Fe, Co and Ni, which are the main components of the metalnanoparticles 10 a, and contribute to an enhancement of the thermalstability of the metal nanoparticles 10 a.

The metal nanoparticles 10 a is formed from, for example, an alloycontaining Fe, Co or Al (aluminum), or an alloy containing Fe, Ni or Si(silicon).

The magnetic metal contained in the metal nanoparticles 10 a includes atleast one selected from the group including Fe, Co and Ni, andparticularly, a Fe-based alloy, a Co-based alloy, a FeCo-based alloy,and a FeNi-based alloy are preferred because these alloys can realizehigh saturation magnetization. Fe-based alloys contain Ni, Mn, Cu andthe like as a second component, and examples thereof include FeNialloys, FeMn alloys, and FeCu alloys. Co-based alloys contain Ni, Mn, Cuand the like as a second component, and examples thereof include CoNialloys, CoMn alloys, and CoCu alloys. FeCo-based alloys include alloyscontaining Ni, Mn, Cu and the like as a second component.

These second components are components that are effective for enhancingthe high-frequency magnetic properties of the metal nanoparticles 10 a.Since FeNi-based alloys have small magnetic anisotropy, these arematerials advantageous for obtaining high magnetic permeability.Particularly, a FeNi alloy having Fe in a proportion of from 40 atom %to 60 atom % has high saturation magnetization and has low magneticanisotropy, and therefore, this alloy is preferred.

Among the magnetic metals, it is particularly preferable to use aFeCo-based alloy. The amount of Co in FeCo is preferably adjusted tofrom 10 atom % to 50 atom %, from the viewpoint of satisfying thermalstability, oxidation resistance, and a saturation magnetization of 2teslas or greater. A more preferred amount of Co in FeCo is in the rangeof from 20 atom % to 40 atom %, from the viewpoint of further increasingthe saturation magnetization.

In regard to the amount of the non-magnetic metal, it is preferable thatthe metal nanoparticles contain the non-magnetic metal in an amount offrom 0.001 atom % to 20 atom % relative to the amount of the magneticmetal. If the content of the non-magnetic metal exceeds 20 atom %, thereis a risk that the saturation magnetization of the magnetic metalnanoparticles may be decreased. As a more preferred amount from theviewpoints of high saturation magnetization and solid solubility, it ispreferable to incorporate the non-magnetic metal in an amount in therange of from 0.001 atom % to 5 atom %, and more preferably from 0.01atom % to 5 atom %.

As the crystal structure of the metal nanoparticles 10 a, abody-centered cubic lattice structure (bcc), a face-centered cubiclattice structure (fcc), and a hexagonal close-packed structure (hcp)can be considered, and each of them has unique features. The bccstructure is advantageous in that since a composition having a largeproportion of a Fe-based alloy has the bcc structure, the bcc structurecan be easily synthesized in a wide variety. The fcc structure isadvantageous in that since the diffusion coefficient of the magneticmetal can be made smaller as compared to that of the bcc structure,thermal stability or oxidation resistance can be made relatively larger.The hcp structure (hexagonal structure) is advantageous in that themagnetic characteristics of the magnetic material can be made to exhibitin-plane uniaxial anisotropy. Since a magnetic metal having the hcpstructure generally has high magnetic anisotropy, it is easy to orientthe magnetic metal, and the magnetic permeability can be made large.Particularly, Co-based alloys easily acquire the hcp structure and arepreferred. In the case of a Co-based alloy, since the alloy canstabilize the hcp structure by containing Cr or Al, it is preferable.

Meanwhile, in a magnetic material having in-plane uniaxial anisotropy,the anisotropic magnetic field in an easy magnetization face ispreferably from 1 Oe to 500 Oe, and more preferably from 10 Oe to 500Oe. This is a preferred range to maintain low loss and high magneticpermeability in the MHz range of 100 kHz or higher. If anisotropy is toolow, the ferromagnetic resonance frequency occurs at a low frequency,and a large loss occurs in the MHz range, which is not preferable.

On the other hand, if anisotropy is high, the ferromagnetic resonancefrequency is high, and a low loss can be realized. However, the magneticpermeability becomes small, and it is not preferable. The range of ananisotropic magnetic field which can achieve a balance between highmagnetic permeability and low loss is from 1 Oe to 500 Oe, and morepreferably from 10 Oe to 500 Oe.

Meanwhile, in order to induce in-plane uniaxial anisotropy in a magneticmaterial, there are available a method of orienting magnetic particleshaving the hcp structure, as well as a method of inducing magneticanisotropy in any one direction in the plane by means of a magneticfield or strain, by making the crystallinity of the metal nanoparticles10 a as amorphous as possible. For this reason, it is preferable toemploy a composition which can make the magnetic particles amorphous aseasily as possible.

From such a viewpoint, it is preferable that the magnetic metalcontained in the metal nanoparticles 10 a include at least one additivemetal selected from B, Si, C, Ti, Zr, Hf, Nb, Ta, Mo, Cr, Cu and W,which are different from the non-magnetic metal, altogether in an amountof from 0.001 atom % to 25 atom % relative to the total amount of themagnetic metal, non-magnetic metal and additive metal, and that at leasttwo of the magnetic metal, the non-magnetic metal, and the additivemetal form a solid solution with each other.

At least a portion of the surface of the metal nanoparticles 10 a may becovered with a coating layer. The coating layer is preferably an oxide,a composite oxide, a nitride, a carbide or a fluoride, which contains atleast one magnetic metal which is a constituent component of the metalnanoparticles 10 a. When the coating layer contains at least onemagnetic metal which is a constituent component of the metalnanoparticles 10 a, the adhesiveness between the metal nanoparticles 10a and the coating layer is enhanced, and thermal stability and oxidationresistance are enhanced.

Furthermore, the coating layer is more preferably an oxide, a compositeoxide, a nitride, a carbide or a fluoride, which contains at least onenon-magnetic metal selected from the group including Mg, Al, Si, Ca, Zr,Ti, Hf, Zn, Mn, Ba, Sr, Cr, Mo, Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn,and rare earth elements. When the metal nanoparticles 10 a contain atleast one non-magnetic metal selected from the group including Mg, Al,Si, Ca, Zr, Ti, Hf, Zn, Mn, Ba, Sr, Cr, Mo, Ag, Ga, Sc, V, Y, Nb, Pb,Cu, In, Sn, and rare earth elements, the coating layer is morepreferably composed of an oxide, a composite oxide, a nitride, a carbideor a fluoride, which contains at least one of the same non-magneticmetals as the non-magnetic metals which is one constituent component ofthe metal nanoparticles 10 a. Thereby, the adhesiveness between themetal nanoparticles 10 a and the coating layer can be enhanced, andfurther, the thermal stability and oxidation resistance of the magneticmaterial can be enhanced.

Meanwhile, in the constitution of the coating layer such as describedabove, among an oxide, a composite oxide, a nitride, a carbide and afluoride, particularly an oxide and a composite oxide are morepreferred. This is based on the viewpoints of the ease of formation ofthe coating layer, oxidation resistance, and thermal stability.

Furthermore, the oxide or composite oxide coating layer is an oxide orcomposite oxide containing at least one magnetic metal, which is aconstituent component of the metal nanoparticles 10 a, and is morepreferably an oxide or composite oxide containing at least onenon-magnetic metal selected from the group including Mg, Al, Si, Ca, Zr,Ti, Hf, Zn, Mn, Ba, Sr, Cr, Mo, Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn,and rare earth elements.

This non-magnetic metal is an element which has small standard Gibbsenergy of formation of the oxide and is easily oxidized, and thenon-magnetic metal can easily form a stable oxide. The oxide coatinglayer that is formed from an oxide or composite oxide containing atleast one or more of these non-magnetic metals can have enhancedadhesiveness and bindability to the metal nanoparticles 10 a, and canalso enhance the thermal stability and oxidation resistance of the metalnanoparticles 10 a.

Among the non-magnetic metals, Al and Si are preferred because theseelements can easily form solid solutions with Fe, Co and Ni, which aremain components of the magnetic metal particles, and contribute to anenhancement of the thermal stability of the metal nanoparticles 10 a. Acomposite oxide containing plural kinds of non-magnetic metals alsoencompasses a solid solution form. The coating layer that covers atleast a portion of the surfaces of the metal nanoparticles 10 a not onlyenhances oxidation resistance of the metal nanoparticles 10 a in theinterior, but also can enhance the electrical resistivity of thecomposite magnetic particles. By increasing the electrical resistivity,the eddy current loss at high frequencies can be suppressed, and thehigh frequency properties of magnetic permeability can be enhanced. Forthis reason, the coating layer preferably has high electricalresistivity, and for example, it is preferable that the coating layerhave a resistance value of 1 mΩ·cm or higher.

As the coating layer is thicker, the electrical resistivity of themagnetic particles 10 increases, and the thermal stability and oxidationresistance of the metal nanoparticles 10 a are also increased. However,if the coating layer is made too thick, the magnetic interaction betweenthe metal nanoparticles 10 a is easily broken, and individual metalnanoparticles 10 a are likely to behave magnetically independently. Thisis not preferable from the viewpoints of the magnetic permeability andthe high frequency properties of magnetic permeability. Furthermore,when the coating layer is thickened, the proportion of the magneticcomponents contained in the magnetic particles 10 decreases.Accordingly, the saturation magnetization of the magnetic particles 10is lowered, and the magnetic permeability is decreased, which is notpreferable. In order for the coating layer to have appropriately largeelectrical resistivity, to have individual metal nanoparticles 10 amagnetically interacted, and to increase the saturation magnetization ofthe magnetic particles 10, it is more preferable that the coating layerhave an average thickness of from 0.1 nm to 5 nm.

Furthermore, the intermediate phase 10 b that is present between themetal nanoparticles 10 a and contains at least one non-magnetic metalselected from Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, Ba, Sr, Cr, Mo, Ag,Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn, and rare earth elements, and any oneof oxygen (O), nitrogen (N) and carbon (C), preferably has an electricalresistivity of 1 mΩ·cm or higher.

These non-magnetic metals are preferably elements which have smallstandard Gibbs energy of formation of the oxide and are easily oxidized,and are preferably metals that can easily form stable oxides. When ametal, a semiconductor, an oxide, a nitride, a carbide or a fluoride,which contains such a non-magnetic metal, is present between the metalnanoparticles 10 a, it is preferable because the electrical insulationproperties between the metal nanoparticles 10 a can be further enhanced,and the thermal stability of the metal nanoparticles can be enhanced.

Furthermore, it is preferable that the intermediate phase 10 b of ametal, a semiconductor, an oxide, a nitride, a carbide or a fluoridecontain at least one of the magnetic metals described above. When themetal, semiconductor, oxide, nitride, carbide or fluoride contains atleast one of the same metals as the magnetic metals contained in themetal nanoparticles 10 a, the thermal stability and oxidation resistanceare enhanced. Furthermore, when a ferromagnetic component is presentbetween the metal nanoparticles 10 a, the magnetic interaction betweenthe magnetic metal nanoparticles is strengthened. For this reason, themetal nanoparticles 10 a and the intermediate phase 10 b can behave asan aggregate magnetically, and the magnetic permeability and the highfrequency properties of magnetic permeability can be enhanced.

Furthermore, similarly, when the intermediate phase 10 b of a metal, asemiconductor, an oxide, a nitride, a carbide or a fluoride contains atleast one of the same non-magnetic metals as the non-magnetic metalscontained in the metal nanoparticles 10 a, thermal stability andoxidation resistance are enhanced. Therefore, it is preferable.

Meanwhile, when the intermediate phase contains at least one each of themagnetic metals and the non-magnetic metals that are contained in themetal nanoparticles, it is preferable that the atomic ratio ofnon-magnetic metal/magnetic metal in the intermediate phase be largerthan the atomic ratio of non-magnetic metal/magnetic metal contained inthe metal nanoparticles. This is because the metal nanoparticles can beblocked by an “intermediate phase having a large ratio of non-magneticmetal/magnetic metal,” which has high oxidation resistance and thermalstability, and the oxidation resistance and thermal stability of themetal nanoparticles can be effectively increased. Furthermore, it ispreferable that the content of oxygen contained in the intermediatephase be larger than the content of oxygen of the metal nanoparticles.This is because the metal nanoparticles can be blocked by an“intermediate phase having a high oxygen concentration and having highoxidation resistance and thermal stability,” and the oxidationresistance and thermal stability of the metal nanoparticles can beeffectively increased.

Among a metal, a semiconductor, an oxide, a nitride, a carbide and afluoride, an oxide is more preferred from the viewpoint of thermalstability.

FIG. 8 is a schematic diagram of the magnetic material of a firstmodification of the current embodiment. The intermediate phase 10 b of ametal, an oxide, a nitride, a carbide or a fluoride may be in the formof particles, as illustrated in FIG. 8.

According to the current modification, the material surrounding themagnetic particles 10 is not particularly limited, and the material maybe, for example, air, an oxide or a resin. Also, in the currentmodification, the space between the metal nanoparticles 10 a and theintermediate phase 10 b of the particles is filled with the samematerial as the material surrounding the magnetic particles 10.

FIG. 9 is a schematic diagram of the magnetic material of a secondmodification of the current embodiment. In the current modification, thespace between the metal nanoparticles 10 a and the intermediate phase 10b of the particles is filled with another intermediate phase 10 c of amaterial that is different from any of the intermediate phase 10 b andthe material surrounding the magnetic particles 10. The combination ofthe material of the intermediate phase 10 c and the material surroundingthe magnetic particles 10 is not particularly limited.

The intermediate phase 10 b that is in the form of particles ispreferably such that the particles have a smaller particle size than theparticle size of the metal nanoparticles 10 a. At this time, theparticles may be oxide particles, may be nitride particles, may becarbide particles, or may be fluoride particles. However, from theviewpoint of thermal stability, the particles are more preferably oxideparticles. In the following descriptions, the case in which theintermediate phase 10 b is oxide particles will be taken as an examplein all cases.

Meanwhile, a more preferred state of existence of the oxide particles isa state in which the oxide particles are uniformly and homogeneouslydispersed between the metal nanoparticles 10 a. Thereby, more uniformmagnetic characteristics and dielectric characteristics can be expected.These oxide particles not only enhance the oxidation resistance and thesuppression of the aggregation of the metal nanoparticles 10 a, that is,the thermal stability of the metal nanoparticles 10 a, but alsoelectrically separate the metal nanoparticles 10 a, so that theelectrical resistivity of the magnetic particles 10 and the magneticmaterial can be increased. When the electrical resistivity of themagnetic material is increased, the eddy current loss at highfrequencies can be suppressed, and the high frequency properties ofmagnetic permeability can be enhanced. For this reason, the oxideparticles preferably have high electrical resistivity, and for example,it is preferable that the oxide particles have an electrical resistivityof 1 mΩ·cm or higher.

The oxide particles contain at least one non-magnetic metal selectedfrom the group including Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, Ba, Sr, Cr,Mo, Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn, and rare earth elements. Thesenon-magnetic metals are elements which have small standard Gibbs energyof formation of the oxide and are easily oxidized, and the non-magneticmetals can easily form stable oxides.

Further, the when the metal nanoparticles 10 a include a coating layer,it is preferable that the ratio of non-magnetic metal/magnetic metal(atomic ratio) in these oxide particles be larger than the ratio ofnon-magnetic metal/magnetic metal (atomic ratio) in the coating layerthat covers the metal nanoparticles 10 a. As such, since the proportionof the non-magnetic metal is large, the oxide particles are morethermally stable than the coating layer.

For this reason, when such oxide particles are present in at least somepart between the metal nanoparticles 10 a, the electrical insulationproperties between the metal nanoparticles 10 a can be further enhanced,and the thermal stability of the magnetic metal nanoparticles can beenhanced.

Meanwhile, the oxide particles may not contain a magnetic metal, butmore preferably, the oxide particles contain a magnetic metal. Apreferred amount of the magnetic metal to be included is 0.001 atom % ormore, and more preferably 0.01 atom % or more, relative to the amount ofthe non-magnetic metal. This is because if the oxide particles do notcontain any magnetic metal at all, the constituent components of thecoating layer that covers the surfaces of the metal nanoparticles 10 aand the oxide particles completely differ from each other, and it is notmuch preferable from the viewpoints of adhesiveness and strength.Furthermore, there is also a possibility that thermal stability mayrather deteriorate. Furthermore, if the oxide particles that are presentbetween the metal nanoparticles do not contain the magnetic metal atall, it is difficult for the metal nanoparticles to magneticallyinteract with each other, and it is not preferable from the viewpointsof the magnetic permeability and the high frequency properties ofmagnetic permeability.

Therefore, the oxide particles are more preferably a constituentcomponent of the metal nanoparticles 10 a, and preferably contain atleast one magnetic metal, which is a constituent component of the oxidecoating layer. More preferably, it is preferable that the ratio ofnon-magnetic metal/magnetic metal (atomic ratio) in the oxide particlesbe larger than the ratio of non-magnetic metal/magnetic metal (atomicratio) in the oxide coating layer.

Meanwhile, the oxide particles are more preferably oxide particles whichcontain a non-magnetic metal that is of the same type as thenon-magnetic metal contained in the metal nanoparticles 10 a, and of thesame type as the non-magnetic metal contained in the oxide coatinglayer. It is because when the oxide particles are oxide particlescontaining a non-magnetic metal of the same type, the thermal stabilityand oxidation resistance of the magnetic metal nanoparticles are furtherenhanced.

Meanwhile, the thermal stability enhancing effect, the electricalinsulation effect, and the adhesiveness and strength enhancing effect ofthe oxide particles as described above are exhibited particularly whenthe average particle size of the metal nanoparticles 10 a is small, andit is particularly effective when the particle size of the oxideparticles is smaller than the particle size of the metal nanoparticles10 a. Furthermore, the volume filling ratio of the metal nanoparticles10 a is preferably from 30 vol % to 80 vol % relative to the totalvolume of the magnetic particles 10 which are particle aggregates. Thevolume filling ratio is more preferably from 40 vol % to 80 vol %, andeven more preferably from 50 vol % to 80 vol %.

Thereby, the distance between the metal nanoparticles 10 a that arecontained in the magnetic particles 10 is inevitably shortened, and themetal nanoparticles 10 a magnetically strongly interact with each otherand behave as particle aggregates magnetically. Thus, the magneticpermeability can be made large. Furthermore, since the metalnanoparticles 10 a are not physically perfectly connected, themicroscopic eddy current loss can be reduced, and the high frequencyproperties of magnetic permeability can be enhanced.

In order to exhibit this effect more effectively, it is preferable thatthe average interparticle distance of the metal nanoparticles 10 acontained in the magnetic particles 10 be preferably from 0.1 nm to 10nm, and more preferably from 0.1 nm to 5 nm. The interparticle distanceas used herein means the distance of the gap between two metalnanoparticles 10 a, along a line connecting the center of one metalnanoparticle 10 a and the center of another metal nanoparticle 10 a.When the surface of the metal nanoparticles 10 a is covered by a coatinglayer, the interparticle distance refers to the distance of the gapbetween the outermost surface of the surface coating layer of one metalnanoparticle 10 a and the outermost surface of the coating layer ofanother metal nanoparticle 10 a.

Thereby, the metal nanoparticles 10 a magnetically interact with eachother, and behave as particle aggregates (composite magnetic particles)magnetically, so that the magnetic permeability can be increased.Furthermore, since the metal nanoparticles 10 a are not physicallyperfectly connected, the microscopic eddy current loss can be reduced,and the high frequency characteristics of magnetic permeability can beenhanced.

In this specification, such a particle aggregate of the metalnanoparticles 10 a is regarded as one magnetic particle 10, but thereare occasions in which two or more particle aggregates join together inthe process of forming particle aggregates. Even in such cases, when aboundary line is drawn between particle aggregates, and the averageparticle size of one particle aggregate segregated by this boundary lineis from 50 nm to 50 μm, the segregated particle aggregate is acceptableas a particle aggregate, in the case of spherical aggregates.Furthermore, in the case of flat-shaped or rod-shaped particleaggregates, when the average height (in the case of a rod shape, theaverage diameter) is from 10 nm to 2 μm, and more preferably, when theaverage height is from 10 nm to 100 nm, and the average aspect ratio is5 or greater, and more preferably 10 or greater, the segregated particleaggregate is acceptable as a particle aggregate.

Furthermore, there are occasions in which a portion of one particleaggregate is bound to another particle aggregate. In even this case, ifthe conditions such as described above are satisfied when a boundaryline is drawn on one particle aggregate and a portion of anotherparticle aggregate, the particle aggregate is acceptable as a particleaggregate having a morphology of one particle aggregate bound to aportion of another particle aggregate.

Furthermore, there are also occasions in which particle aggregateshaving a distorted shape other than a plate shape, an oblate ellipsoid,a rod shape, or an ellipsoid of revolution, are obtained. When the ratioof the long dimension and the short dimension, that is, the aspect ratiois 5 or greater, and more preferably 10 or greater, and the shortdimension is from 10 nm to 2 μm, and more preferably, the shortdimension is from 10 nm to 100 nm, the particle aggregate is acceptableas a particle aggregate having a distorted shape.

Furthermore, when a material other than the metal nanoparticles 10 a,which is contained in the particle aggregates, and the materialsurrounding the particle aggregates are the same, the outer periphery ofthe particle aggregates is ambiguous and not easily recognizable. Evenin such a case, if it can be confirmed by structural observation by TEMor SEM that the metal nanoparticles 10 a aggregate and segregate in acertain material, and particle aggregates having an average shortdimension of from 10 nm to 2 μm, and an average aspect ratio of 5 orgreater are formed, the particle aggregate is acceptable as a particleaggregate. As discussed above, when the distance between the metalnanoparticles 10 a contained in the particle aggregates is 10 nm orless, the effect offered by the current modification is enhanced.Therefore, the distance between aggregated and unevenly distributedmetal nanoparticles is preferably 10 nm or less.

Furthermore, when a portion of one particle aggregate is bound toanother particle aggregate, and also in the case of a particle aggregatehaving a distorted shape other than a plate shape, an oblate ellipsoid,a rod shape, or an ellipsoid of revolution, if the height and aspectratio described above are satisfied when a boundary line is drawn, theparticle aggregate is acceptable as a particle aggregate. As one of themethods of drawing boundary lines, a method of drawing a boundary lineat a site where the average value of the interparticle distance betweenone metal nanoparticle 10 a and another metal nanoparticle 10 a presentin the vicinity is 10 nm or greater, and preferably 100 nm or greater,may be used.

Meanwhile, this is just one of possible methods after all, and inreality, it is preferable to determine, by structural observation by TEMor SEM to an extent based on common sense, a region in which there arerelatively more metal nanoparticles 10 a as compared with thesurroundings, and to draw a boundary line as one particle aggregate.Furthermore, it is preferable that the magnetic particles 10 have ashape with a large aspect ratio, from the viewpoints of high magneticpermeability and satisfactory high frequency magnetic characteristics.

Flat-shaped and rod-shaped magnetic particles are preferred, and theaverage height (in the case of a rod shape, the average diameter) ispreferably from 10 nm to 2 μm, and even more preferably, the averageheight (in the case of a rod shape, the average diameter) is from 10 nmto 100 nm. A larger average aspect ratio is more preferred, and anaverage aspect ratio of 5 or greater is preferred. The average aspectratio is more preferably 10 or greater. These are appropriate sizes forminimizing the sum of the eddy current loss and the hysteresis loss inthe MHz range of 100 kHz or higher.

Furthermore, a higher electrical resistivity of the magnetic particlesis more preferred; however, even if the intermediate phase 10 bcontained in the magnetic particles 10 has higher resistivity, generallyas the volume ratio of the metal nanoparticles 10 a increases, theelectrical resistivity of the magnetic particles 10 decreases. This isbecause in reality, the metal nanoparticles 10 a do not isolatethemselves, but partially form a network or aggregate. Such an effectbecomes conspicuous as the particle size of the metal nanoparticles 10 ais smaller, and the volume ratio is larger.

On the other hand, if the volume ratio of the metal nanoparticles 10 ais decreased, the content of the magnetic component contained in themagnetic particles 10 decreases. Therefore, a decrease in the saturationmagnetization is caused, and it is not preferable. As such, theelectrical resistivity and saturation magnetization of the magneticparticles 10 are in a trade-off relationship to some extent.

Ideally, when the volume proportion of the metal nanoparticles in thecomposite magnetic particles is from 30 vol % to 80 vol %, morepreferably from 40 vol % to 80 vol %, and even more preferably from 50vol % to 80 vol %, it is preferable if the electrical resistivity of themagnetic particles 10 can be maximized. However, in practice, theelectrical resistivity is from 100 μΩ·cm to 100 mΩ·cm.

That is, a preferred range of electrical resistivity in which a balanceis achieved between high saturation magnetization and high electricalresistivity is from 100 μΩ·cm to 100 mΩ·cm. Meanwhile, such magneticparticles 10 are capable of inducing in-plane uniaxial anisotropy bymeans of the magnetic field or strain, which is preferable. As discussedabove, in a magnetic material having in-plane uniaxial anisotropy, theanisotropic magnetic field in an easy magnetization plane is preferablyfrom 1 Oe to 500 Oe, and more preferably from 10 Oe to 500 Oe. This is arange necessary to maintain low loss and high magnetic permeability inthe MHz range of 100 kHz or higher.

Meanwhile, the space between the magnetic particles 10 which areparticle aggregates may be, for example, filled with a resin.

Eighth Embodiment

The magnetic material of the current embodiment is the same as theseventh embodiment, except that a composite phase of a metal phasecontaining at least one magnetic metal selected from the group includingFe, Co and Ni, and a second intermediate phase containing at least onenon-magnetic metal selected from Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, Ba,Sr, Cr, Mo, Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn, and rare earthelements, and any one of oxygen (O), nitrogen (N) and carbon (C), ispresent between the magnetic particles of the seventh embodiment.Therefore, further descriptions on the matters that overlap with theseventh embodiment will not be repeated.

FIG. 10 is a schematic diagram of the magnetic material of the currentembodiment. Between magnetic particles which are particle aggregates,there is present a composite phase which is composed of core-shell typemagnetic particles containing magnetic metal particles (metal phase) 20containing at least one magnetic metal selected from the group includingFe, Co and Ni, a coating layer (second intermediate phase) 22 thatcovers at least a portion of the surfaces of the magnetic metalparticles 20. The coating layer (second intermediate phase) 22 is asecond intermediate phase containing at least one non-magnetic metalselected from Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, Ba, Sr, Cr, Mo, Ag,Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn, and rare earth elements, and any oneof oxygen (O), nitrogen (N) and carbon (C).

The characteristics required from the second intermediate phase are thesame as those for the intermediate phase according to the seventhembodiment.

The magnetic metal particles (metal phase) 20 are preferably particleshaving an average particle size of from 5 nm to 50 nm, and among others,particularly, particles having an average particle size of from 5 nm to30 nm are preferred. When the magnetic material contains a compositephase which includes particles having an average particle size in thisrange, the magnetic interaction between individual magnetic particles 10can be effectively enhanced, while electrical resistivity is maintainedhigh. Also, the proportion of the magnetic metal contained in theentirety of the magnetic material can be effectively increased, whileelectrical resistivity is maintained high. Thereby, the magneticpermeability and saturation magnetization can be effectively enhanced,while the high-frequency magnetic properties of the magnetic materialare maintained.

Furthermore, it is preferable that the magnetic metal particles 20contain at least one magnetic metal selected from the group includingFe, Co and Ni, and that the coating layer 22 contain at least onenon-magnetic metal selected from Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, Ba,Sr, Cr, Mo, Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn, and rare earthelements. Thereby, the magnetic interaction between individual magneticparticles 10 can be more effectively enhanced, while electricalresistivity is maintained high. Also, the proportion of the magneticmetal contained in the entirety of the magnetic material can be moreeffectively increased, while electrical resistivity is maintained high.Thus, it is preferable.

In core-shell type magnetic particles, it is more preferable if thecore-shell type magnetic particles are core-shell type magneticparticles in which the magnetic metal particles 20 contain at least onemagnetic metal selected from the group including Fe, Co and Ni, and atleast one non-magnetic metal selected from Mg, Al, Si, Ca, Zr, Ti, Hf,Zn, Mn, Ba, Sr, Cr, Mo, Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn, and rareearth elements, and the coating layer 22 contains at least one of themagnetic metals described above and at least one of the non-magneticmetals described above. It is because thereby, the components of themagnetic metal particles 20 and the components of the coating layer 22have similar compositions in the core-shell type magnetic particles, andtherefore, the adhesiveness between the magnetic metal particles 20 andthe interface between the magnetic metal particles and the coating layer22 is increased, so that the thermal stability of the magnetic materialis increased.

When the magnetic material adopts a configuration such as describedabove, the sum of the eddy current loss and the hysteresis loss in theMHz range of 100 kHz or higher can be extremely minimized, and themagnetic material can have high magnetic permeability and highsaturation magnetization.

FIG. 11 is a schematic diagram of a modification of the magneticmaterial of the current embodiment. As illustrated in FIG. 9, thecomposite phase is composed of plural magnetic metal particles (metalphase) 20, and an adhesive layer (insulating layer) 24 that fills thespace between these plural magnetic metal particles 20.

Even in the current modification, the sum of the eddy current loss andthe hysteresis loss in the MHz range of 100 kHz or higher can beextremely minimized, and the magnetic material can have high magneticpermeability and high saturation magnetization.

Ninth Embodiment

The method for producing a magnetic material of the current embodimentincludes a step of synthesizing plural metal nanoparticles that have anaverage particle size of from 1 nm to 1 μm and contain at least onemagnetic metal selected from the group including Fe, Co and Ni; a stepof forming an intermediate phase containing at least one non-magneticmetal selected from Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, Ba, Sr, Cr, Mo,Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn, and rare earth elements, and anyone of oxygen (O), nitrogen (N) and carbon (C), on at least a portion ofthe surfaces of the metal nanoparticles; and a step of integrating themetal nanoparticles and the intermediate phase, and thereby formingparticle aggregates that have an average short dimension of from 10 nmto 2 μm (more preferably of from 10 nm to 100 nm) and an average aspectratio of 5 or greater (more preferably of from 10 or greater), and avolume filling ratio of the metal nanoparticles of from 40 vol % to 80vol %.

The current embodiment relates to a method for producing the magneticmaterial of the seventh embodiment. Therefore, further descriptions onthe matters that overlap with the seventh embodiment will not berepeated.

The method for producing a magnetic material of the current embodimentis a method for producing a magnetic material having magnetic particles,which are particle aggregates including metal nanoparticles that have anaverage particle size of from 1 nm to 20 nm, and more preferably of from1 nm to 10 nm and contain at least one magnetic metal selected from thegroup including Fe, Co and Ni, and an intermediate phase that is presentbetween the metal nanoparticles and contains at least one non-magneticmetal selected from Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, Ba, Sr, Cr, Mo,Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn, and rare earth elements, and anyone of oxygen (O), nitrogen (N) and carbon (C), the particle aggregateshaving a morphology with an average short dimension of from 10 nm to 2μm (more preferably of from 10 nm to 100 nm) and an average aspect ratioof 5 or greater (more preferably of from 10 or greater), and the volumefilling ratio of the metal nanoparticles being from 40 vol % to 80 vol %relative to the total volume of the particle aggregates.

Further, the method is a production method appropriate for synthesizinga magnetic material in which the average interparticle distance betweenthe metal nanoparticles is from 0.1 nm to 5 nm.

That is, the magnetic material is synthesized by a step of synthesizingmetal nanoparticles containing at least one magnetic metal selected fromthe group including Fe, Co and Ni, and a non-magnetic metal; a step offorming an intermediate phase (coating layer) of an oxide on at least aportion of the surfaces of the metal nanoparticles; and a step ofsubjecting the magnetic particles coated with an oxide, to a compositeintegration treatment.

According to the current embodiment, first, the process begins with astep of synthesizing metal nanoparticles containing at least onemagnetic metal selected from the group including Fe, Co and Ni, and anon-magnetic metal. At this time, the step of synthesizing the metalnanoparticles is not particularly limited, and synthesis is carried outby, for example, a water atomization method, a gas atomization method, aheat plasma method, a CVD method, a laser abrasion method, or anin-liquid dispersion method.

However, when the metal nanoparticles are synthesized, metalnanoparticles having a smaller particle size of from 1 nm to 1 μm arepreferred, and 1 nm to 100 nm are more preferred, because two-phaseseparation of the magnetic metal and the intermediate phase can beeasily accelerated in the subsequent step. The metal nanoparticles withaverage particle size of from 10 nm to 100 nm are much more preferable.For this reason, it is preferable to use a heat plasma method that iscapable of performing the synthesis easily and in a large amount. Theintermediate phase is, for example, an oxide, a semiconductor, anitride, a carbide, or a fluoride, but in this specification, anintermediate phase of an oxide will be taken as an example in thefollowing descriptions.

In the case of using a heat plasma method, first, a magnetic metalpowder having an average particle size of several micrometers and anon-magnetic metal, which are raw materials, are sprayed together with acarrier gas into a plasma generated in a chamber of a high frequencyinduction heat plasma apparatus. Thereby, metal nanoparticles containinga magnetic metal can be easily synthesized.

Subsequently, the process proceeds to a step of forming an intermediatephase (coating layer) of an oxide on at least a portion of the metalnanoparticles. In this step, the method of coating with an oxide is notparticularly limited, but the process may be carried out by liquid phasecoating or a partial oxidation method.

The partial oxidation method is a method of synthesizing metalnanoparticles containing a magnetic metal and a non-magnetic metal,subsequently subjecting the metal nanoparticles to partial oxidationunder appropriate oxidation conditions, and thereby precipitating anoxide containing the non-magnetic metal on the surface of the metalnanoparticles to form a coating layer.

This technique is based on causing the precipitation of an oxide throughdiffusion, and when compared with a liquid phase coating method, themetal nanoparticles and the interface between the metal nanoparticlesand the oxide coating layer strongly adhere to each other, so that thethermal stability and oxidation resistance of the metal nanoparticlesare enhanced, which is preferable. There are no particular limitationson the conditions for partial oxidation, but it is preferable to oxidizethe metal nanoparticles in an oxidative atmosphere of O₂, CO₂ or thelike, at an adjusted oxygen concentration, and at a temperature in therange of room temperature to 1,000° C.

Meanwhile, the present process may be carried out during the step ofsynthesizing metal nanoparticles. That is, core-shell type metalnanoparticles containing an oxide coating layer containing anon-magnetic metal may be synthesized on the surfaces of the metalnanoparticles, by controlling the process conditions in the middle ofthe process of synthesizing metal nanoparticles with a heat plasma.

Through the steps described above, core-shell type magnetic metalnanoparticles in which the surfaces of magnetic metal particles arecoated with a non-magnetic metal oxide coating layer, can besynthesized. That is, a two-phase separated structure of metals andoxides at a nanoscale level can be realized.

Subsequently, the process proceeds to a step of integrating the metalnanoparticles and the intermediate phase, that is, a step of subjectingmetal nanoparticles coated with an oxide, to a composite integrationtreatment. In this step, metal nanoparticles that are obtained byrapidly cooling the synthesis product are subjected to a compositeintegration treatment by using a high-power mill apparatus. Thereby,particle aggregates can be obtained relatively easily.

The high-power mill apparatus is not limited in the selection of thetype, as long as it is an apparatus capable of applying stronggravitational acceleration, but for example, a high-power planetary millapparatus which is capable of applying a gravitational acceleration ofseveral ten G's, or the like is preferred. If possible, it is preferableto apply a gravitational acceleration of 50 G or greater, and morepreferably 100 G or greater.

Furthermore, when a high-power mill is used, it is preferable to performthe process in an inert gas atmosphere in order to maximally suppressoxidation of the magnetic nanoparticles. Also, if a powder is subjectedto a composite integration treatment in a dry mode, the compositeintegration treatment can be easily carried out; however, the structureis likely to become coarse, and collection of the particles isdifficult. Moreover, the shape of particles thus obtainable is alsospherical in many cases.

On the other hand, if the composite integration treatment is carried outin a wet mode using a liquid solvent, it is preferable becausecoarsening of the structure is suppressed, and a flat shape is easilyobtained. A more preferred method is to perform a treatment ofsuppressing the coarsening of the structure, while acceleratingcomposite integration, by carrying out the treatment both in a dry modeand in a wet mode.

Particle aggregates can be easily synthesized by using such a technique;however, depending on the synthesis conditions, making the shape of theparticle aggregates into a flat shape with a large aspect ratio is alsoreadily realizable, and it is preferable. When composite particleshaving a large aspect ratio are produced, shape-induced magneticanisotropy can be imparted, and by aligning the directions of the axesof easy magnetization into one direction, the magnetic permeability andthe high frequency characteristics of magnetic permeability can beenhanced, which is preferable.

Meanwhile, even if the particles undergo slight oxidation, the particlescan be reduced by subjecting the particles to a heat treatment in areducing atmosphere. Furthermore, the step of forming a coating layer ofan oxide on at least a portion of the surfaces of the metalnanoparticles may also be carried out in the present step of subjectingmetal nanoparticles to a composite integration treatment.

That is, in regard to the present composite integration treatment step,the composite integration treatment can be carried out while forming anoxide, by controlling the treatment conditions, specifically, bycontrolling the oxygen partial pressure in the atmosphere, or the typeof the liquid solvent used at the time of wet mixing. As such, theprocess of forming an oxide may be carried out after the metalnanoparticles are synthesized, and may also be carried out during thestep of synthesizing metal nanoparticles, or may also be carried outduring the step of performing a composite integration treatment.

Meanwhile, the method of synthesizing a magnetic material such asdescribed above is not intended to be limited to the methods describedabove, and the magnetic material can also be synthesized by, forexample, a method such as described below. For example, a method ofsynthesizing a nanogranular structure can be used, that is, ananogranular structure in which plural magnetic metal nanoparticles arefilled in a matrix, by a thin film process or the like, detaching thethin film, and pulverizing the thin film into particle aggregates.

First, a magnetic metal, and an oxide, a semiconductor, a carbide, anitride or a fluoride, which constitutes the intermediate phasecontaining a non-magnetic metal, are simultaneously formed into a film.Hereinafter, in the current embodiment, an intermediate phase composedof an oxide will be described.

The film-forming method is not particularly limited as long as it is amethod of carrying out two-phase separation of metals and oxides at ananoscale level, but a sputtering method, a vapor deposition method, aphysical vapor deposition (PVD) method and the like are preferred. Byusing such a method, a magnetic thin film of particle aggregates(nanogranular thin film) containing magnetic metal nanoparticles thathave an average particle size of from 1 nm to 20 nm, and an oxide thatis present between magnetic metal nanoparticles, and contains at leastone each of non-magnetic metals and the magnetic metals described above,can be synthesized.

The thickness of the deposited film is a thickness capable ofmaintaining a nanoscale composite structure, and is not particularlylimited. However, in general, if the thickness is increased, thestructure tends to be rough, and therefore, a thickness of 1 μm or lessis preferred. The magnetic thin film of particle aggregates that hasbeen deposited on a substrate surface is detached from the substrate andcollected, and the collected thin film fragments are pulverized. Themethod of pulverizing the thin film fragments is not particularlylimited, but for example, methods of using a rotary ball mill, avibratory ball mill, a stirring ball mill, a planetary mill, a jet mill,and mortar pulverization may be used.

In this manner, a magnetic material having magnetic particles, which areparticle aggregates containing metal nanoparticles that have an averageparticle size of from 1 nm to 20 nm, and more preferably of from 1 nm to10 nm and contain at least one magnetic metal selected from the groupincluding Fe, Co and Ni, and an intermediate phase that is presentbetween the metal nanoparticles and contain at least one non-magneticmetal selected from Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, Ba, Sr, Cr, Mo,Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn, and rare earth elements, and anyone of oxygen (O), nitrogen (N) and carbon (C), the particle aggregateshaving a morphology with an average short dimension of from 10 nm to 2μm (more preferably of from 10 nm to 100 nm) and an average aspect ratioof 5 or greater (more preferably of from 10 or greater), and the volumefilling ratio of the metal nanoparticles being from 40 vol % to 80 vol %relative to the total volume of the particle aggregates, can beproduced.

Meanwhile, the particle aggregates are produced to exhibit a morphologyhaving an average short dimension of from 10 nm to 2 μm (more preferablyof from 10 nm to 100 nm) and an average aspect ratio of 5 or greater(more preferably of from 10 or greater), by appropriately controllingthe film-forming conditions or pulverization conditions for the magneticthin film of particle aggregates. Furthermore, the particle aggregatesare produced such that the volume filling ratio of the metalnanoparticles is from 40 vol % to 80 vol % relative to the total volumeof the particle aggregates.

Tenth Embodiment

The device of the current embodiment is a device including one of themagnetic materials described in the above-described embodiments.Therefore, further descriptions on the matters that overlap with theembodiments described above will not be repeated.

The device of the current embodiment is, for example, a high-frequencymagnetic component such as an inductor, a choke coil, a filter, or atransformer, an antenna substrate/component, or a an electromagneticwave absorber.

An application which can best take advantage of the features of themagnetic materials of the embodiments described above is an inductorelement for power inductors. The magnetic material can easily exhibiteffects when applied to a power inductor to which a high current isapplied, at a frequency in the MHz range of 100 kHz or higher, forexample, in the 10 MHz band.

Specifications that are required from a magnetic material for powerinductors include high magnetic permeability, as well as low magneticlosses (mainly low eddy current loss and low hysteresis loss), andsatisfactory direct current superimposition characteristics. In powerinductors used at a frequency band of lower than 100 kHz, existingmaterials such as a silicon steel sheet, a Sendust, an amorphous ribbon,a nanocrystalline ribbon, and MnZn-based ferrite are being used;however, a magnetic material which sufficiently satisfies thespecifications required for power inductors used at a frequency band of100 kHz or higher does not exist.

For example, the metal-based materials described above are inadequatefor use at frequencies of 100 kHz or higher because the materials havelarge eddy current losses at high frequencies. Furthermore, since MnZnferrite, or NiZn ferrite for coping with high frequency bands have lowsaturation magnetization, their direct current superimpositioncharacteristics are poor, and the materials are not preferable. That is,there has been no magnetic material hitherto, which can satisfy all ofhigh magnetic permeability, low magnetic losses, and satisfactory directcurrent superimposition characteristics in the MHz range of 100 kHz orhigher, for example, in the 10 MHz band, and there is a strong demandfor the development of such a magnetic material.

From such viewpoint, the magnetic materials of the embodiments can besaid to be materials that are excellent particularly in high magneticpermeability, low magnetic losses, and satisfactory direct currentsuperimposition characteristics. First, the eddy current loss can bereduced by means of high electrical resistivity; however, the magneticmaterials described above in particular contain an oxide, asemiconductor, a carbide, a nitride or a fluoride, which has highelectrical resistivity, between magnetic particles or metalnanoparticles. For this reason, electrical resistivity can be increased,and it is preferable.

Furthermore, the hysteresis loss can be reduced by decreasing thecoercive force (or magnetic anisotropy) of the magnetic material. In themagnetic materials described above, the magnetic anisotropy ofindividual magnetic particles is low, and also, the total magneticanisotropy can be further reduced as individual magnetic metal particlesmagnetically interact with each other. That is, in the magneticmaterials described above, both the eddy current loss and the hysteresisloss can be sufficiently reduced.

Furthermore, in order to realize satisfactory direct currentsuperimposition characteristics, it is important to suppress magneticsaturation, and in order to do so, a material having high saturationmagnetization is preferred. Even from this viewpoint, the magneticmaterials of the embodiments described above are preferred because thematerials can acquire high total saturation magnetization by selectingmagnetic metal particles having high saturation magnetization in theinterior. Meanwhile, in general, magnetic permeability increases as thesaturation magnetization increases, and as magnetic anisotropydecreases. Accordingly, the magnetic materials of the embodimentsdescribed above can also have high magnetic permeability.

From the viewpoints described above, the magnetic materials of theembodiments described above can particularly easily exhibit the effectswhen applied as inductor elements in power inductors to which a highcurrent is applied, at a frequency in the MHz range of 100 kHz orhigher, for example, in the 10 MHz band.

Meanwhile, the magnetic materials of the embodiments described above canbe used not only as high-permeability components such as inductorelements, but also as electromagnetic wave absorbers, by varying thefrequency bands of use. Generally, a magnetic material adopts high μ″near the ferromagnetic resonance frequency. However, in the magneticmaterials of the embodiments described above, since various magneticlosses except for the ferromagnetic resonance loss, for example, theeddy current loss and the domain wall resonance loss, can be suppressedas much as possible, the materials can have small μ″ and large μ′ in afrequency band that is sufficiently lower than the ferromagneticresonance frequency. That is, the magnetic materials are preferredbecause just one material can be used in high-permeability components,and also as an electromagnetic wave absorber, simply by varying thefrequency band of use.

On the other hand, a material that is developed as an electromagneticwave absorber is usually designed to maximize μ″ by summing up variouslosses including the ferromagnetic resonance loss and various magneticlosses (the eddy current loss, the domain wall resonance loss, and thelike). Therefore, it is difficult to use a material that has beendeveloped as an electromagnetic wave absorber, in high-permeabilitycomponents for inductor elements or antenna apparatuses (high μ′ and lowμ″) at any of all frequency bands.

A magnetic material may be subjected to various processing treatments soas to be applied to devices such as described above. For example, in thecase of a sintered body, the material is subjected to mechanical workingsuch as polishing or grinding, and in the case of a powder, the materialis subjected to mixing with a resin such as an epoxy resin orpolybutadiene. If necessary, the materials are further subjected tosurface treatments.

FIG. 12A, FIG. 12B, FIG. 13A, FIG. 13B, and FIG. 14 are conceptualdiagrams of the devices of the current embodiment. When thehigh-frequency magnetic component is an inductor, a choke coil, afilter, or a transformer, a coiling treatment is achieved.

The most fundamental structures include the inductor element shown inFIG. 12A, in which a ring-shaped magnetic material is provided with acoil wound around the material, and the inductor element shown in FIG.12B, in which a rod-shaped magnetic material is provided with a coilwound around the material.

Further examples include the chip inductor element shown in FIG. 13A, inwhich coils and magnetic materials have been integrated, and the planarinductor element shown in FIG. 13B. In the case of FIG. 13A, the devicemay be fabricated into a laminate.

Furthermore, FIG. 14 shows an inductor element having a transformerstructure.

FIG. 12A to FIG. 14 merely illustrate representative structures, and inreality, the structure or dimension may be varied in accordance with theapplication and required inductor element characteristics.

According to the devices of the current embodiment, devices havingexcellent characteristics can be realized by using a magnetic materialwhich has a high real part of magnetic permeability (μ′) and a lowimaginary part of magnetic permeability (μ″) particularly in the MHzrange of 100 kHz or higher, and has high strength, high saturationmagnetization, high thermal stability, and high oxidation resistance.

Thus far, embodiments of the present application have been describedwhile making reference to specific examples. The embodiments describedabove are only for illustrative purposes, and are not intended to limitthe present application by any means. Furthermore, the constituentelements of the various embodiments may also be appropriately combined.

In the explanations of the embodiments, descriptions on the parts thatare not directly needed in the explanation of the present application inconnection with the magnetic material, the method for producing amagnetic material, the inductor element and the like, were not repeated.However, necessary elements that are related to the magnetic material,the method for producing a magnetic material, and the inductor elementcan be appropriately selected and used.

In addition, all magnetic materials, methods for producing a magneticmaterial, and inductor elements that include the elements of the presentapplication and can be appropriately designed and modified by a personhaving ordinary skill in the art, are to be included in the scope of thepresent application. The scope of the present application is to bedefined by the scope of the claims and equivalents thereof.

EXAMPLES

Hereinafter, Examples 1 to 13 of the present application will bedescribed in detail by making a comparison with Comparative Examples 1to 5. In regard to the magnetic materials obtained by Examples andComparative Examples described below, the shape, average particle size(or average height), average aspect ratio, and composition of themagnetic particles; the composition of the first oxide; the compositionof the second oxide; the composition of the third oxide; and thecomposition of the eutectic structure are presented in Table 1.Meanwhile, the measurement of the average particle size (or averageheight) of the magnetic particles is carried out by calculating theaverage value of plural particles based on a TEM observation or a SEMobservation. Meanwhile, the magnetic particles of Example 7 are particleaggregates in which metal nanoparticles are dispersed at a high density,and the average particle size of the metal nanoparticles inside themagnetic particles is determined comprehensively based on a TEMobservation, and the crystal grain size determined by XRD (utilizingScherrer's formula). Also, the composition analysis of microstructuresis carried out based on an EDX analysis.

Example 1

First, spherical FeCoAl magnetic particles are synthesized by a wateratomization method. Subsequently, a SiO₂ coating layer (a first coatinglayer of a first oxide) is formed on these magnetic particles accordingto a sol-gel method. Thereafter, the magnetic particles having a SiO₂coating layer formed thereon, and B₂O₃ particles (oxide particles of asecond oxide) are sufficiently mixed in a ball mill. Thereafter, themixed particles are subjected to press molding and a heat treatment at600° C. in a vacuum. Thus, a magnetic material for evaluation isobtained.

The same magnetic material as that illustrated in FIG. 1 of the firstembodiment is obtained. In the magnetic material, a first oxide and asecond oxide are present in addition to magnetic particles, and an oxidephase having an eutectic structure produced from the first oxide and thesecond oxide is present between the magnetic particles.

Example 2

An AlFeCo—O oxide, which becomes a third oxide, is formed as a coatinglayer (second coating layer) on the surfaces of the FeCoAl magneticparticles, by subjecting the magnetic particles of Example 1 to apartial oxidation treatment. The subsequent treatments are the same asthose performed in Example 1.

The same magnetic material as the modification illustrated in FIG. 3 ofthe first embodiment is obtained. In the magnetic material, a firstoxide and a second oxide are present, in addition to magnetic particlescoated with a third oxide, and an oxide phase having an eutecticstructure produced from the first oxide and the second oxide is presentbetween the magnetic particles.

Example 3

A plasma is generated by introducing argon as a gas for plasmageneration into a chamber of a high frequency induction heat plasmaapparatus at a rate of 40 L/min. An Fe powder having an average particlesize of 5 μm, a Co powder having an average particle size of 5 μm, andan Al powder having an average particle size of 3 μm, which are rawmaterials, are sprayed together with argon (carrier gas) into thisplasma in the chamber at a rate of 3 L/min. FeCoAl magnetic particlesobtained by rapid cooling are subjected to a flattening treatment usinga planetary mill which uses ZrO₂ balls and a ZrO₂ pot, in an argon (Ar)atmosphere at about 2000 rpm. Thereafter, the flattened powder thusobtained is sufficiently heat treated in a hydrogen (H₂) atmosphere, andthus homogenous flat magnetic particles are obtained. Subsequently, theflat magnetic particles thus obtained are subjected to a partialoxidation treatment, and thereby an AlFeCo—O oxide coating layer (secondcoating layer), which serves as a third oxide, is formed on the surfacesof the FeCoAl magnetic particles. The subsequent treatments are the sameas those performed in Example 1.

In the magnetic material, a first oxide and a second oxide are present,in addition to magnetic particles coated with a third oxide, and anoxide phase having an eutectic structure produced from the first oxideand the second oxide is present between the magnetic particles.

Example 4

The production is carried out in the same manner as in Example 3, exceptthat the Co powder used in Example 3 is changed to a Ni powder having anaverage particle size of 3 μm, and the Al powder is changed to a Sipowder having an average particle size of 5 μm. Meanwhile, in themagnetic material, a first oxide and a second oxide are present, inaddition to magnetic particles coated with a third oxide, and an oxidephase having an eutectic structure produced from the first oxide and thesecond oxide is present between the magnetic particles.

Example 5

An AlFeCo—O oxide coating layer is formed on the surfaces of the flatmagnetic particles of Example 3, and then a SiO₂ coating layer (firstoxide) is formed on these magnetic particles according to a sol-gelmethod. Subsequently, the magnetic particles having a SiO₂ coating layerformed thereon and B₂O₃ particles (second oxide) are sufficiently mixedin a ball mill. Thereafter, the mixed particles are subjected to pressmolding and a heat treatment for a long time at 600° C. in a vacuum, andthus the first oxide and the second oxide are completely eutecticallymelted. Thereby, a magnetic material for evaluation is obtained.Meanwhile, in the magnetic material, magnetic particles coated with athird oxide are present, and an oxide phase having an eutectic structureproduced from a first oxide and a second oxide is present between themagnetic particles, but the first oxide and the second oxide are notpresent.

Example 6

An AlFeCo—O oxide coating layer is formed on the surfaces of the flatmagnetic particles produced in Example 3, and then a SiO₂ coating layer(first oxide) is formed on these magnetic particles according to asol-gel method. Subsequently, the magnetic particles having a SiO₂coating layer formed thereon and B₂O₃ particles (second oxide) aresufficiently mixed in a ball mill. The subsequent heat treatment is notcarried out. These mixed particles are subjected to press molding, andthereby, a magnetic material for evaluation is obtained. Meanwhile, inthe magnetic material, a first oxide and a second oxide are present, inaddition to magnetic particles coated with a third oxide. An oxide phasehaving an eutectic structure does not exist.

Example 7

A plasma is generated by introducing argon as a gas for plasmageneration into a chamber of a high frequency induction heat plasmaapparatus at a rate of 40 L/min. An Fe powder having an average particlesize of 5 μm, a Co powder having an average particle size of 5 μm, andan Al powder having an average particle size of 3 μm, which are rawmaterials, are sprayed together with argon (carrier gas) into thisplasma in the chamber at a rate of 3 L/min. FeCoAl magnetic particlesobtained by rapid cooling are subjected to a partial oxidationtreatment, and thereby FeCoAl magnetic particles coated with Al—Fe—Co—Oare obtained. These FeCoAl magnetic particles coated with Al—Fe—Co—O aresubjected to a flattening treatment using a planetary mill which usesZrO₂ balls and a ZrO₂ pot, in an Ar atmosphere at about 2000 rpm.Thereafter, the flattened powder thus obtained is sufficiently heattreated in a H₂ atmosphere at a low temperature of 200° C., and a SiO₂coating layer (first oxide) is formed on these magnetic particlesaccording to a sol-gel method. Subsequently, the magnetic particleshaving a SiO₂ coating layer formed thereon (particle aggregate) and B₂O₃particles (second oxide) are sufficiently mixed in a ball mill.Thereafter, the mixed particles are subjected to press molding and aheat treatment at 600° C. in a vacuum. Thus, a magnetic material forevaluation is obtained.

The magnetic particles are in the form of particle aggregates in whichFeNiAl particles having an average particle size of 8 nm (metalnanoparticles) are dispersed at a high density in an AlFeNiO matrix(intermediate phase). Meanwhile, in the magnetic material, a first oxideand a second oxide are present in addition to magnetic particles, and anoxide phase having an eutectic structure produced from the first oxideand the second oxide is present between the magnetic particles.

Example 8

The production is carried out in the same manner as in Example 7, exceptthat the Co powder used in Example 7 is changed to a Ni powder having anaverage particle size of 3 μm, and the Al powder is changed to a Sipowder having an average particle size of 5 μm. The magnetic particlesare in the form of particle aggregates in which FeNiSi particles havingan average particle size of 8 nm (metal nanoparticles) are dispersed ata high density in a SiFeNiO matrix (intermediate phase). Meanwhile, inthe magnetic material, a first oxide and a second oxide are present inaddition to magnetic particles, and an oxide phase having an eutecticstructure produced from the first oxide and the second oxide is presentbetween the magnetic particles.

Example 9

The production is carried out in the same manner as in Example 7, exceptthat the Co powder used in Example 7 is changed to a Ni powder having anaverage particle size of 3 μm, the Al powder is changed to a Si powderhaving an average particle size of 5 μm, and the mixed particles thusobtained are subjected to press molding and a heat treatment for a longtime at 600° C. in a vacuum. The magnetic particles are in the form ofparticle aggregates in which FeNiSi particles having an average particlesize of 8 nm (metal nanoparticles) are dispersed at a high density in aSiFeNiO matrix (intermediate phase). Meanwhile, in the magneticmaterial, magnetic particles are present, and an oxide phase having aneutectic structure produced from a first oxide and a second oxide ispresent between the magnetic particles, but the first oxide and thesecond oxide are not present.

Example 10

The production is carried out in the same manner as in Example 7, exceptthat the Co powder used in Example 7 is changed to a Ni powder having anaverage particle size of 3 μm, the Al powder is changed to a Si powderhaving an average particle size of 5 μm, and a magnetic material forevaluation is obtained by press molding the mixed particles that havebeen sufficiently mixed in a ball mill, but without performing a heattreatment. The magnetic particles are in the form of particle aggregatesin which FeNiSi particles having an average particle size of 8 nm (metalnanoparticles) are dispersed at a high density in a SiFeNiO matrix(intermediate phase). Meanwhile, in the magnetic material, a first oxideand a second oxide are present in addition to magnetic particles. Anoxide phase having an eutectic structure does not exist.

Example 11

First, spherical FeBAl magnetic particles are synthesized by a wateratomization method. The subsequent treatments are the same as those usedin Example 1. Meanwhile, at the time of molding, the particles areoriented while a magnetic field of 1 T is applied, and press molding isperformed. The magnetic particles are in an amorphous state, and areoriented by a magnetic field. Meanwhile, in the magnetic material, afirst oxide and a second oxide are present in addition to magneticparticles, and an oxide phase having an eutectic structure produced fromthe first oxide and the second oxide is present between the magneticparticles.

Example 12

First, spherical CoAl magnetic particles are synthesized by a wateratomization method. Subsequently, the magnetic particles are subjectedto a partial oxidation treatment, and thereby an AlCo—O oxide, which isa third oxide, is formed on the surfaces of the CoAl magnetic particles.The subsequent treatments are the same as those used in Example 1. Thecrystal structure of the magnetic particles is a hexagonal structure,and the magnetic particles are oriented by a magnetic field. Meanwhile,at the time of molding, the magnetic particles are oriented while amagnetic field of 1 T is applied, and press molding is performed.Meanwhile, in the magnetic material, a first oxide and a second oxideare present, in addition to magnetic particles coated with a thirdoxide, and an oxide phase having an eutectic structure produced from thefirst oxide and the second oxide is present between the magneticparticles.

Example 13

A plasma is generated by introducing argon as a gas for plasmageneration into a chamber of a high frequency induction heat plasmaapparatus at a rate of 40 L/min. An Fe powder having an average particlesize of 5 μm, a Co powder having an average particle size of 5 μm, andan Al powder having an average particle size of 3 μm, which are rawmaterials, are sprayed together with argon (carrier gas) into thisplasma in the chamber at a rate of 3 L/min. FeCoAl magnetic particlesobtained by rapid cooling are subjected to a heat treatment to controlthe particle size, and then to a partial oxidation treatment. Thus, anAlFeCo—O oxide, which is a third oxide, is formed on the surfaces of theFeCoAl magnetic particles. Subsequently, a SiO₂ coating layer (firstoxide) is formed on the magnetic particles thus obtained, according to asol-gel method. Thereafter, the magnetic particles having a SiO₂ coatinglayer formed thereon are sufficiently mixed with B₂O₃ particles (secondoxide) in a ball mill. Subsequently, the mixed particles are subjectedto press molding and to a heat treatment at 600° C. in a vacuum, andthereby, a magnetic material for evaluation is obtained. Meanwhile, inthe magnetic material, a first oxide and a second oxide are present, inaddition to magnetic particles coated with a third oxide, and an oxidephase having an eutectic structure produced from the first oxide and thesecond oxide is present between the magnetic particles.

Comparative Example 1

A magnetic material for evaluation is obtained by forming a SiO₂ coatinglayer (first oxide) on the spherical FeCoAl magnetic particlessynthesized in Example 1 according to a sol-gel method, and subjectingthe magnetic particles to press molding and then to a heat treatment at600° C. in a vacuum. Meanwhile, in the magnetic material, only a firstoxide is present in addition to magnetic particles.

Comparative Example 2

A magnetic material for evaluation is obtained by sufficiently mixingthe spherical FeCoAl magnetic particles synthesized in Example 1 withB₂O₃ particles (second oxide) in a ball mill, and subjecting themagnetic particles to press molding and then to a heat treatment at 600°C. in a vacuum. Meanwhile, in the magnetic material, only a second oxideis present in addition to magnetic particles.

Comparative Example 3

A SiO₂ coating layer (first oxide) is formed on the spherical FeCoAlmagnetic particles synthesized in Example 1 according to a sol-gelmethod, and then the magnetic particles having a SiO₂ coating layerformed thereon are sufficiently mixed with B₂O₃ particles (second oxide)in a ball mill. At this time, the B₂O₃ particles are incorporated in asufficiently small amount as compared with the amount of SiO₂, so thatthe B₂O₃ particles would be completely melted with SiO₂ in thesubsequent heat treatment. Subsequently, the mixed particles thusobtained are subjected to press molding and to a heat treatment at 600°C. in a vacuum, and thereby, a magnetic material for evaluation isobtained. Meanwhile, in the magnetic material, magnetic particles arepresent, and a first oxide, and an oxide phase having an eutecticstructure produced from the first oxide and a second oxide is presentbetween the magnetic particles, but a second oxide is not present.

Comparative Example 4

An AlFeCo—O oxide coating layer (first coating layer) is formed on thesurfaces of the flat magnetic particles obtained in Example 3, and thena SiO₂ coating layer (first oxide) is formed on these magnetic particlesaccording to a sol-gel method. The magnetic particles are subjected topress molding and then to a heat treatment at 600° C. in a vacuum, andthereby, a magnetic material for evaluation is obtained. Meanwhile, inthe magnetic material, only a first oxide is present in addition tomagnetic particles coated with a third oxide (first coating layer).

For the materials for evaluation of Examples 1 to 13 and ComparativeExamples 1 to 4, the real part of magnetic permeability (μ′), thepermeability loss (μ−tan δ=μ″/μ′×100(%)), and change over time in thereal part of magnetic permeability (μ″) after 100 hours are evaluated bythe following methods. The evaluation results are presented in Table 2.

1) Real part of magnetic permeability μ′, and permeability loss (μ−tanδ=μ″/μ′×100(%))

The magnetic permeability of a ring-shaped sample is measured using animpedance analyzer. The real part μ′ and the imaginary part μ″ aremeasured at two frequencies of 100 kHz and 10 MHz. For sphericalparticles, the value at 100 kHz is measured, and for flat-shapedparticles, the values at 100 kHz and 10 MHz are measured. Furthermore,the permeability loss, μ−tan δ, is calculated by the formulaμ″/μ′×100(%).

2) Change over time in real part of magnetic permeability μ′ after 100hours

A sample for evaluation is heated for 100 hours at 200° C. in theatmosphere, and then the real part of magnetic permeability μ′ ismeasured again. Thus, the change over time (real part of magneticpermeability μ′ after heating for 100H/real part of magneticpermeability μ′ before heating) is determined.

TABLE 1 Magnetic particles Average particle Oxide phase size(Spherical), Average (eutectic average height aspect First oxide Secondoxide Third oxide structure) Shape (Flat) (μm) ratio CompositionComposition Composition Composition Composition Example 1 Spherical 25ca. 1 Fe—Co—Al Si—O B—O — Si—B—O Example 2 Spherical 24 ca. 1 Fe—Co—AlSi—O B—O Al—FeCo—O Si—B—O Example 3 Flat 0.09 110 Fe—Co—Al Si—O B—OAl—FeCo—O Si—B—O Example 4 Flat 0.07 200 Fe—Ni—Si Si—O B—O Si—FeNi—OSi—B—O Example 5 Flat 0.09 110 Fe—Co—Al — — Al—FeCo—O Si—B—O Example 6Flat 0.09 110 Fe—Co—Al Si—O B—O Al—FeCo—O — Example 7 Flat 0.08 120Fe—Ni—Al Si—O B—O — Si—B—O Example 8 Flat 0.07 150 Fe—Ni—Si Si—O B—O —Si—B—O Example 9 Flat 0.07 150 Fe—Ni—Si — — — Si—B—O Example 10 Flat0.07 150 Fe—Ni—Si Si—O B—O — — Example 11 Spherical 22 ca. 1 Fe—B—AlSi—O B—O — Si—B—O Example 12 Spherical 23 ca. 1 Co—Al Si—O B—O Al—Co—OSi—B—O Example 13 Spherical 0.1 ca. 1 Fe—Co—Al Si—O B—O Al—FeCo—O Si—B—OComparative Spherical 25 ca. 1 Fe—Co—Al Si—O — — — Example 1 ComparativeSpherical 25 ca. 1 Fe—Co—Al — B—O — — Example 2 Comparative Spherical 25ca. 1 Fe—Co—Al Si—O — — Si—B—O Example 3 Comparative Flat 0.09 110Fe—Co—Al Si—O — Al—FeCo—O — Example 4

TABLE 2 Characteristics of high frequency magnetic material Proportionof change over time of real part of magnetic Real part of magneticPermeability permeability μ′ after 100 hr permeability, μ′ loss, μ-tanδ(%) at 200° C. 100 kHz 10 MHz 100 kHz 10 MHz 100 kHz 10 MHz Example 1 10— 2 — 0.85 — Example 2 9 — 2 — 0.89 — Example 3 10 10 <0.1 <0.1 0.880.88 Example 4 13 13 <0.1 <0.1 0.89 0.89 Example 5 11 11 <0.1 <0.1 0.860.86 Example 6 11 11 <0.1 <0.1 0.84 0.84 Example 7 10 10 <0.1 <0.1 0.880.88 Example 8 11 11 <0.1 <0.1 0.88 0 88 Example 9 11 11 <0.1 <0.1 0.870.87 Example 10 11 11 <0.1 <0.1 0.86 0.86 Example 11 13 — 1 — 0.84 —Example 12 12 — 1 — 0.83 — Example 13 5.2 5.0 <0.1 0.1 0.85 0.85Comparative 9 — 5 — 0.70 — Example 1 Comparative 8 — 6 — 0.68 — Example2 Comparative 7 — 4 — 0.73 — Example 3 Comparative 8 8 0.1 0.1 0.72 0.72Example 4

As is obvious from Table 1, the magnetic material according to Example 1to Example 13 are such that in the case of spherical particles, theaverage particle size is from 50 nm to 50 μm, and in the case offlat-shaped particles, the average height is from 10 nm to 100 nm, andthe average aspect ratio is 10 or greater.

Furthermore, the magnetic metal contained in the magnetic particles isFeCo in Examples 1, 2, 3, 5, 6 and 13; FeNi in Examples 4, 7, 8, 9, and10; Fe in Example 11; and Co in Example 12. Furthermore, thenon-magnetic metal contained in the magnetic particles is Al in Examples1 to 3, 5 to 7, and 11 to 13; and Si in Examples 4 and 8 to 10.Furthermore, the combination of the first oxide and the second oxide isa combination of a Si—O oxide and a B—O oxide. In Examples 1 to 4, 7 to8, and 11 to 13, three oxides such as Si—O of a first oxide, B—O of asecond oxide, and Si—B—O of an eutectic structure are present betweenthe magnetic particles, and in Examples 2 to 4 and 12 to 13, a thirdoxide is further present. In Example 5, two components such as a thirdoxide AlFeCoO and an eutectic structure of Si—B—O are present betweenthe magnetic particles. In Example 6, three components such as a thirdoxide AlFeCoO, a first oxide Si—O, and a second oxide B—O are presentbetween the magnetic particles. In Example 9, only an eutectic structureSi—B—O is present between the magnetic particles. In Example 10, twocomponents such as a first oxide Si—O and a second oxide B—O are presentbetween the magnetic particles.

On the other hand, in Comparative Example 1, the magnetic particles arethe same as the magnetic particles of Example 1, but only Si—O of afirst oxide is present between the magnetic particles. In ComparativeExample 2, the magnetic particles are the same as the magnetic particlesof Example 1, but only B—O of a second oxide is present between themagnetic particles. In Comparative Example 3, the magnetic particles arethe same as the magnetic particles of Example 1, but only two componentssuch as Si—O of a first oxide and Si—B—O of an eutectic structure arepresent between the magnetic particles. Furthermore, in ComparativeExample 4, the magnetic particles are almost the same as the magneticparticles of Examples 3, 5 and 6, but only two components such as Si—Oof a first oxide and AlFeCoO of a third oxide are present between themagnetic particles.

Table 2 presents the real part of magnetic permeability (μ′), thepermeability loss (μ−tan δ=μ″/μ′×100(%)), and the change over time inthe real part of magnetic permeability (μ′) after 100 hours at 200° C.As is obvious from Table 2, it can be seen that the magnetic materialsrelated to Example 1 to Example 13 have excellent magnetic properties ascompared with the materials of Comparative Examples.

FIG. 13 is a diagram presenting the frequency characteristics of themagnetic permeability (μ′ and μ″) of Example 3. It can be seen that μ″is almost zero up to 100 MHz (that is, μ″ is also almost zero), and μ″steeply rises from near 200 MHz. That is, it can be seen that themagnetic material has high magnetic permeability and low losses in ahigh frequency band of from 100 kHz to 100 MHz. Meanwhile, in the caseof such a material having a steep initial rise of μ″, when the frequencyband is selected to be a higher frequency band, for example, when afrequency band of 1 GHz to 10 GHz is selected, the magnetic material canalso be used as an electromagnetic wave absorber.

Examples 1, 2 and 11 to 13 have higher magnetic permeability and lowerlosses, and have smaller changes over time in the real part of magneticpermeability after 100 hours, as compared with Comparative Examples 1 to3. Furthermore, Examples 3 to 10 have higher magnetic permeability andlower losses, and have smaller changes over time in the real part ofmagnetic permeability after 100 hours, as compared with ComparativeExamples 4 and 5. These materials all include magnetic particlescontaining at least one magnetic metal selected from the group includingFe, Co and Ni and at least one non-magnetic metal selected from Al andSi; and a Si—O coating layer as a first oxide and B—O particles as asecond oxide, which are present between these magnetic particles, or aSi—B—O eutectic structure of the first oxide and the second oxide, or aSi—O coating layer as a first oxide, B—O particles as a second oxide,and a Si—B—O eutectic structure, and the materials can thereby realizeexcellent characteristics.

That is, when a magnetic material is surrounded by two oxides of aneutectic reaction system, an eutectic structure thereof, or two oxidesof an eutectic reaction system and an eutectic structure thereof, astate of being thermally stable and having high oxidation resistance canbe maintained. It is speculated that thereby, high magnetic permeabilityand low losses can be realized, and these characteristics are maintainedeven after a heat treatment at a high temperature.

Furthermore, it is contemplated that since a material that is evenstrong in terms of strength is acquired by having an eutectic structure,the occurrence of cracking and damage at the time of heating and coolingis suppressed as much as possible, and accordingly, oxidation of themagnetic particles is also effectively suppressed.

Thus, it is understood that the magnetic materials according to Examples1 to 13 have high real parts of magnetic permeability (μ′) and lowimaginary parts of magnetic permeability (μ″) in the MHz range of 100kHz or higher, and have high saturation magnetization, high thermalstability, and high oxidation resistance.

Next, the following Example 14 to Example 22 will be described incomparison with Comparative Example 5. In the magnetic materialsobtained by Examples and Comparative Example described below, the shape,average height, average aspect ratio, and electrical resistivity of themagnetic particles; the shape, composition, particle size, fillingratio, and average interparticle distance of the metal nanoparticles;and the composition of the intermediate phase are presented in Table 3.Meanwhile, the measurement of the average height of the magneticparticles is carried out by calculating the average value of pluralparticles based on a TEM observation and a SEM observation. Meanwhile,the magnetic particles of the Examples are particle aggregates in whichmetal nanoparticles are dispersed at a high density, and the averageparticle size of the metal nanoparticles inside the magnetic particlesis determined comprehensively based on a TEM observation, and thecrystal grain size determined by XRD (utilizing Sherrer's formula).Also, the composition analysis of microstructures is carried out basedon an EDX analysis.

Example 14

A plasma is generated by introducing argon as a gas for plasmageneration into a chamber of a high frequency induction heat plasmaapparatus at a rate of 40 L/min. An Fe powder having an average particlesize of 5 μm, a Ni powder having an average particle size of 3 μm, and aSi powder having an average particle size of 5 μm, which are rawmaterials, are sprayed together with argon (carrier gas) into thisplasma in the chamber at a rate of 3 L/min. FeNiSi magnetic particlesobtained by rapid cooling are subjected to a partial oxidationtreatment, and thus, FeNiSi magnetic particles coated with Si—Fe—Ni—Oare obtained. These FeNiSi magnetic particles coated with Si—Fe—Ni—O aresubjected to a flattening and integrating treatment by a planetary millusing ZrO₂ balls and a ZrO₂ pot in an Ar atmosphere at about 2000 rpm.Subsequently, a H₂ heat treatment is carried out at a low temperature of200° C., and the particles thus obtained are molded. Thus, a magneticmaterial for evaluation is obtained. The same magnetic material as thatshown in FIG. 7 of the seventh embodiment is obtained. The magneticmaterial thus obtainable is composed of flat particle aggregates inwhich spherical metal nanoparticles are filled at a high density in anoxide matrix (intermediate phase).

Example 15

The production is carried out in the same manner as in Example 14,except that the Si powder used in Example 14 is changed to an Al powderhaving an average particle size of 3 μm.

Example 16

The production is carried out in the same manner as in Example 14,except that the Ni powder used in Example 14 is changed to a Co powderhaving an average particle size of 5 μm, and the Si powder is changed toan Al powder having an average particle size of 3 μm.

Example 17

The production is carried out in the same manner as in Example 14,except that the Ni powder used in Example 14 is changed to a Co powderhaving an average particle size of 5 μm.

Example 18

The production is carried out in the same manner as in Example 17,except that the feed ratio of the Ni powder and the Fe powder in Example17 is adjusted such that the filling ratio of the FeNi magnetic metalnanoparticles finally obtainable is 78 vol %. Meanwhile, the fillingratio of the FeNi magnetic metal nanoparticles finally obtainable in thecase of Example 17 is 41 vol %.

Example 19

The production is carried out in the same manner as in Example 17,except that the FeNi magnetic metal nanoparticles finally obtainable bycontrolling the conditions of the flattening and integrating treatmentcarried out by a planetary mill using ZrO₂ balls and a ZrO₂ pot inExample 17, are produced into rod-shaped particles having an aspectratio of 4.

Example 20

The production is carried out in the same manner as in Example 17,except that B is solved when FeCoSi particles are synthesized in Example17, and the filling ratio of the magnetic metal particles is adjusted to50 vol %.

Example 21

The production is carried out in the same manner as in Example 14,except that the powders fed in Example 14 are changed to a Co powderhaving an average particle size of 5 μm, an Al powder having an averageparticle size of 3 μm, and a Cr powder having an average particle sizeof 10 μm, and the hcp-structured CoCrAl magnetic metal nanoparticlesfinally obtainable by controlling the conditions of the flattening andintegrating treatment carried out by a planetary mill using ZrO₂ ballsand a ZrO₂ pot, are produced into rod-shaped particles having an aspectratio of 10.

Example 22

The production is carried out in the same manner as in Example 14,except that a composite phase in which FeCoAl magnetic metalnanoparticles (metal phase) are dispersed in an Al—FeCo—O matrix (secondintermediate phase), is present between the individual flat compositeparticles of Example 14. This composite phase is synthesized by thefollowing method. First, argon is introduced at a rate of 40 L/min as agas for plasma generation into a chamber of a high frequency inductionheat plasma apparatus to generate a plasma. An Fe powder having anaverage particle size of 5 μm, a Co powder having an average particlesize of 5 μm, and an Al powder having an average particle size of 3 μm,which are raw materials, are sprayed together with argon (carrier gas)into this plasma in the chamber at a rate of 3 L/min. FeCoAl magneticparticles obtained by rapid cooling are subjected to a partial oxidationtreatment, and thus, FeCoAl magnetic particles coated with Al—Fe—Co—Oare obtained. These FeCoAl magnetic particles coated with Al—Fe—Co—O aresubjected to a flattening and integrating treatment by a planetary millusing ZrO₂ balls and a ZrO₂ pot in an Ar atmosphere at about 2000 rpm.Thereafter, a H₂ heat treatment is carried out at a low temperature of200° C., and thus a composite phase is obtained. This composite phaseand the flat particle aggregates synthesized in Example 14 are mixed ina ball mill, the particles thus obtained are molded, and thus a magneticmaterial for evaluation is obtained.

Example 23

The production is carried out in the same manner as in Example 14,except that core-shell type magnetic particles (composite phase) inwhich the surfaces of FeCoAl magnetic metal nanoparticles (metal phase)are covered with an Al—FeCo—O oxide coating layer (second intermediatephase), are present between the individual flat particle aggregates ofExample 14. The core-shell type magnetic nanoparticles are synthesizedby the following method. First, argon is introduced at a rate of 40L/min as a gas for plasma generation into a chamber of a high frequencyinduction heat plasma apparatus to generate a plasma. An Fe powderhaving an average particle size of 5 μm, a Co powder having an averageparticle size of 5 μm, and an Al powder having an average particle sizeof 3 μm, which are raw materials, are sprayed together with argon(carrier gas) into this plasma in the chamber at a rate of 3 L/min.Also, at the same time with spraying, acetylene gas as a raw materialfor carbon coating is introduced together with a carrier gas into thechamber, and thus particles in which the metal nanoparticles are coatedwith carbon are obtained. These carbon-coated magnetic metalnanoparticles are subjected to a heat treatment at 600° C. under ahydrogen flow at a concentration of 99% at a rate of 500 mL/min, cooledto room temperature, and then taken out in an oxygen-containingatmosphere to oxidize. Thus, core-shell type magnetic particles areobtained. Meanwhile, the coating layer of the core-shell type magneticparticles is formed when the magnetic particles are taken out in anoxygen-containing atmosphere. These core-shell type magnetic particlesand the flat particle aggregates synthesized in Example 14 are mixed ina ball mill, the particles thus obtained are molded, and thereby, amagnetic material for evaluation is obtained.

Comparative Example 5

FeCo particles having a particle size of about 5 μm are pulverized by aplanetary mill using ZrO₂ balls and a ZrO₂ pot in an Ar atmosphere atabout 2000 rpm. Thus, FeCo flat particles having an average height of 90nm and an aspect ratio of 10 are synthesized. Subsequently, theparticles thus obtained are molded, and thus, a magnetic material forevaluation is obtained.

For the materials for evaluation of Examples 14 to 23 and ComparativeExample 5, the real part of magnetic permeability (μ′), the permeabilityloss (μ−tan δ=μ″/μ′×100(%)), and change over time in the real part ofmagnetic permeability after 100 hours are evaluated by the followingmethods. The evaluation results are presented in Table 4.

1) Real part of magnetic permeability μ′, and permeability loss (μ−tanδ=μ″/μ′×100 (%))

The magnetic permeability of a ring-shaped sample is measured using animpedance analyzer. The real part μ′ and the imaginary part μ″ aremeasured at a frequency of 10 MHz. Furthermore, the permeability loss,μ−tan δ, is calculated by the formula μ″/μ′×100(%).

2) Change over time in real part of magnetic permeability μ′ after 100hours

A sample for evaluation is heated for 100 hours at a temperature of 60°C. in the atmosphere, and then the real part of magnetic permeability μ′is measured again. Thus, the change over time (real part of magneticpermeability μ′ after heating for 100H/real part of magneticpermeability μ′ before heating) is determined.

TABLE 3 Magnetic particles (particle aggregates) Configuration Metalnanoparticles Average Average Particle Filling Average Intermediateheight aspect Resistivity size ratio interparticle phase Shape (μm)ratio (μΩ · cm) Shape Composition (nm) (vol %) distance (nm) CompositionExample 14 Flat 0.07 150 500 Spherical Fe—Ni—Si 8 52 1 Si—FeNi—O Example15 Flat 0.08 120 500 Spherical Fe—Ni—Al 8 52 1 Al—FeNi—O Example 16 Flat0.09 100 1000 Spherical Fe—Co—Al 9 41 2 Al—FeCo—O Example 17 Flat 0.09110 1000 Spherical Fe—Co—Si 9 41 2 Si—FeCo—O Example 18 Flat 0.09 115100 Spherical Fe—Co—Si 9 78 — Si—FeCo—O Example 19 Flat 0.09 100 2000Rod Fe—Co—Si 9 41 — Si—FeCo—O (aspect ratio 4) Example 20 Flat 0.08 120800 Spherical Fe—Co—Si—10% B 7 50 1 Si—FeCo—O Example 21 Flat 0.09 1003000 Rod Co—Cr—Al 10 41 — Al—Cr—Co—O (aspect ratio 10) Example 22 Flat0.07 150 500 Spherical Fe—N—iSi 8 52 1 Si—FeNi—O Example 23 Flat 0.07150 500 Spherical Fe—Ni—Si 8 52 1 Si—FeNi—O Comparative Flat 0.09 10 10— — — — — — Example 5

TABLE 4 Characteristics of high frequency magnetic material Real part ofPermeability Proportion of change over magnetic loss, time of real partof magnetic permeability, μ-tanδ (%) permeability μ′ (10 MHz) μ′ (10MHz) (10 MHz) after 100 hr at 60° C. Example 14 11 <0.1 0.92 Example 1511 <0.1 0.92 Example 16 9 <0.1 0.95 Example 17 9 <0.1 0.95 Example 18 14<0.1 0.89 Example 19 12 <0.1 0.97 Example 20 12 <0.1 0.93 Example 21 10<0.1 0.98 Example 22 15 <0.1 0.94 Example 23 14 <0.1 0.96 Comparative 60.1 0.82 Example 5

As is obvious from Table 3, the magnetic materials related to Example 14to Example 23 are such that flat-shaped particle aggregates in whichmetal nanoparticles having an average particle size of from 1 nm to 10nm are filled at a filling ratio of from 40 vol % to 80 vol %, are usedas the magnetic particles. Furthermore, these magnetic particles have ashape with an average height of from 10 nm to 100 nm and an averageaspect ratio of 10 or greater. The resistivity of the magnetic particlesis from 100 μΩ·cm to 100 mΩ·cm.

Furthermore, the magnetic materials of Examples 14 to 17, 20, 22 and 23have an average interparticle distance of the metal nanoparticles offrom 0.1 nm to 5 nm. In Example 19, rod-shaped metal nanoparticles aredispersed inside flat-shaped magnetic particles, and these rod-shapedmetal nanoparticles are oriented to stretch across in the plane of theflat-shaped particle aggregates. In Example 21, rod-shapedhcp-structured (hexagonal) Co-based magnetic metal nanoparticles aredispersed inside flat-shaped magnetic particles, and these rod-shapedmetal nanoparticles are oriented to stretch across in the plane of theflat-shaped particle aggregates. The compositions of the metalnanoparticles are a FeNiSi system for Examples 14, 22 and 23; a FeNiAlsystem for Example 15; a FeCoAl system for Example 16; a FeCoSi systemfor Examples 17, 18 and 19; a CoCrAl system for Example 21; and a systemobtained by adding B to FeCoSi for Example 20. Meanwhile, in Example 22,a composite phase in which FeCoAl magnetic metal nanoparticles (metalphase) are dispersed in an Al—FeCo—O matrix (second intermediate phase),is present between the magnetic particles. In Example 23, core-shelltype magnetic particles in which the surfaces of FeCoAl magnetic metalnanoparticles (metal phase) are covered with an Al—FeCo—O oxide coatinglayer (second intermediate phase), are present between the magneticparticles.

On the other hand, Comparative Example 5 is a material having aflattened structure, but a composite phase of a metal and an oxide doesnot exist, and the material is composed of uniform flat particles formedof FeCo.

Table 4 presents the real part of magnetic permeability (μ′), thepermeability loss (μ−tan δ=μ″/μ′×100(%)), and the change over time inthe real part of magnetic permeability (μ′) after 100 hours at 60° C. Asis obvious from Table 4, it can be seen that the magnetic materialsrelated to Example 14 to Example 23 have excellent magneticcharacteristics as compared with the material of Comparative Example.

That is, Examples 14 to 23 have higher magnetic permeability and lowerlosses, and have smaller changes over time in the real part of magneticpermeability after 100 hours, as compared with Comparative Example 5.The materials of Examples 14 to 23 are each composed of flat-shapedparticle aggregates containing metal nanoparticles that have an averageparticle size of from 1 nm to 10 nm and contain at least one magneticmetal selected from the group including Fe, Co and Ni, and contain anoxide (intermediate phase) that is present between the metalnanoparticles and contain at least one non-magnetic metal selected fromAl and Si, and at least one of the magnetic metals described above, theparticle aggregates having an average short dimension of from 10 nm to100 nm and an average aspect ratio of 10 or greater, and the volumefilling ratio of the metal nanoparticles being from 40 vol % to 80 vol %relative to the total volume of the magnetic particles (particleaggregates).

It is contemplated that when such constitutions are adopted, highmagnetic permeability and low losses can be realized, and theseproperties are maintained even after a heat treatment at a hightemperature. Meanwhile, in Examples 22 and 23, as a composite phase inwhich magnetic metal nanoparticles (metal phase) are dispersed in anoxide matrix (second intermediate phase), or core-shell type magneticparticles in which the surfaces of magnetic metal nanoparticles (metalphase) are covered with an oxide coating layer (second intermediatephase) are present between individual flat particle aggregates (magneticparticles), the magnetic interaction between individual magneticparticles can be effectively increased while electrical resistivity ismaintained high, and the proportion of magnetic metal contained in theentire magnetic material can be effectively increased while electricalresistivity is maintained high.

Thereby, the magnetic permeability and saturation magnetization of amagnetic material can be effectively enhanced while the high frequencymagnetic loss is maintained low. Furthermore, in Example 23, since themagnetic material contains core-shell type magnetic particles havinghigh thermal stability, the magnetic properties after a heat treatmentfor 100 h at 60° C. are maintained high.

Thus, it is understood that the magnetic materials related to Examples14 to 23 have a high real part of magnetic permeability (μ′) and a lowimaginary part of magnetic permeability (μ″) in the MHz range of 100 kHzor higher, and also have high saturation magnetization, high thermalstability, and high oxidation resistance.

While certain embodiments and examples have been described, theseembodiments and examples have been presented byway of example only, andare not intended to limit the scope of the inventions. Indeed, themagnetic material, the method for producing a magnetic material, and theinductor element described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the devices and methods described herein may be made withoutdeparting from the spirit of the inventions. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the inventions.

What is claimed is:
 1. A magnetic material comprising magnetic particleswhich are particle aggregates containing metal nanoparticles and a firstintermediate phase, the particle aggregates having a morphology with anaverage short dimension of from 10 nm to 2 μm and an average aspectratio of 5 or greater, the metal nanoparticles have an average particlesize of from 1 nm to 20 nm and contain at least one magnetic metalselected from a group consists of Fe, Co and Ni, the first intermediatephase is present between the metal nanoparticles and contain at leastone non-magnetic particles selected from Mg, Al, Si, Ca, Zr, Ti, Hf, Zn,Mn, Ba, Sr, Cr, Mo, Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn, and rare earthelements, and the first intermediate phase contain any one of oxygen(O), nitrogen (N) and carbon (C), and the magnetic particles having avolume filling ratio of the metal nanoparticles of from 40 vol % to 80vol % relative to the total volume of the particle aggregates.
 2. Themagnetic material according to claim 1, wherein the metal nanoparticlesfurther contain at least one non-magnetic metal selected from Mg, Al,Si, Ca, Zr, Ti, Hf, Zn, Mn, Ba, Sr, Cr, Mo, Ag, Ga, Sc, V, Y, Nb, Pb,Cu, In, Sn and rare earth elements, and contain at least one additivemetal that is different from the non-magnetic metal and is selected fromB, Si, C, Ti, Zr, Hf, Nb, Ta, Mo, Cr, Cu and W, the non-magnetic metaland the additive metal are respectively contained in an amount of from0.001 atom % to 25 atom % relative to the total amount of the magneticmetal, the non-magnetic metal and the additive metal, and at least twoof the magnetic metal, the non-magnetic metal and the additive metalform a solid solution with each other.
 3. The magnetic materialaccording to claim 1, wherein the crystal structure of the metalnanoparticles is a hexagonal structure.
 4. The magnetic materialaccording to claim 1, wherein the metal nanoparticles are flat-shaped orrod-shaped particles having an average aspect ratio of 2 or greater. 5.The magnetic material according to claim 1, wherein the averageinterparticle distance of the metal nanoparticles is from 0.1 nm to 5nm.
 6. The magnetic material according to claim 1, wherein theelectrical resistivity of the magnetic particles is from 100 μΩ·cm to100 mΩ·cm.
 7. The magnetic material according to claim 1, furthercomprising a composite phase of a metal phase and a second intermediatephase, the composite phase is present between the magnetic particles,the metal phase contains at least one magnetic metal selected from agroup consists of Fe, Co and Ni, and the second intermediate phasecontains at least one non-magnetic metal selected from Mg, Al, Si, Ca,Zr, Ti, Hf, Zn, Mn, Ba, Sr, Cr, Mo, Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Snand rare earth elements, and any one of oxygen (O), nitrogen (N) andcarbon (C).
 8. The magnetic material according to claim 7, wherein thecomposite phase is composed of core-shell type magnetic particlescontaining magnetic metal particles corresponding to the metal phase,and a coating layer corresponding to the second intermediate phase,which covers at least a portion of the surfaces of the magnetic metalparticles; the magnetic metal particles contain at least one magneticmetal selected from a group consists of Fe, Co and Ni, and contain atleast one non-magnetic metal selected from Mg, Al, Si, Ca, Zr, Ti, Hf,Zn, Mn, Ba, Sr, Cr, Mo, Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn and rareearth elements; and the coating layer contains at least one of thenon-magnetic metal described above.
 9. A method for producing a magneticmaterial, the method comprising: synthesizing plural metal nanoparticleshaving an average particle size of from 1 nm to 1 μm and containing atleast one magnetic metal selected from a group consists of Fe, Co andNi; forming an intermediate phase containing at least one non-magneticmetal selected from Mg, Al, Si, Ca, Zr, Ti, Hf, Zn, Mn, Ba, Sr, Cr, Mo,Ag, Ga, Sc, V, Y, Nb, Pb, Cu, In, Sn and rare earth elements, and anyone of oxygen (O), nitrogen (N) and carbon (C), on at least a portion ofthe surfaces of the metal nanoparticles; and forming particle aggregateshaving a morphology with an average short dimension of from 10 nm to 2μm and an average aspect ratio of 5 or greater, and having a volumefilling ratio of the metal nanoparticles of from 40 vol % to 80 vol %,by integrating the metal nanoparticles and the intermediate phase. 10.The method according to claim 9, wherein the synthesizing plural metalnanoparticles is carried out by a heat plasma method.